Handle structured body and attributes

[pellared]

Why

Addresses open-telemetry#4809 (comment) and open-telemetry#4809 (comment).

The type definitions need to be compliant with https://opentelemetry.io/docs/specs/otel/logs/data-model/#type-any

1. Log attributes are different than common (trace, metrics, resource) attributes.
2. Body must handle structure data (not only string).

What

Here is the code containing new types: https://github.com/pellared/opentelemetry-go/blob/strucutred-values/log/value.go

The code adopted from https://github.com/golang/go/blob/master/src/log/slog/value.go to be compliant with https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/data-model.md#type-any

I am not sure if uint64 should be handled or not. I decided to postpone it as we can add it later without introducing any breaking change. Spec issue: open-telemetry/opentelemetry-specification#3836.

Benchmarks

Even a little faster and consuming less memory.

$ benchstat old.txt new.txt
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/log/internal
cpu: Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
                        │    old.txt    │               new.txt                │
                        │    sec/op     │    sec/op     vs base                │
Emit/noop/no_attrs-16      6.494n ± 12%   4.898n ±  4%  -24.57% (p=0.000 n=10)
Emit/noop/3_attrs-16       17.63n ±  9%   12.95n ±  5%  -26.59% (p=0.000 n=10)
Emit/noop/5_attrs-16       24.73n ±  6%   17.89n ±  5%  -27.64% (p=0.000 n=10)
Emit/noop/10_attrs-16      266.9n ±  5%   192.8n ±  3%  -27.74% (p=0.000 n=10)
Emit/noop/40_attrs-16     1307.5n ±  5%   933.2n ±  3%  -28.63% (p=0.000 n=10)
Emit/writer/no_attrs-16    89.00n ±  1%   91.45n ±  6%        ~ (p=0.781 n=10)
Emit/writer/3_attrs-16     231.1n ±  7%   227.3n ±  6%        ~ (p=0.353 n=10)
Emit/writer/5_attrs-16     265.5n ±  4%   269.1n ±  4%        ~ (p=0.436 n=10)
Emit/writer/10_attrs-16    735.7n ±  6%   630.8n ± 10%  -14.27% (p=0.000 n=10)
Emit/writer/40_attrs-16    3.156µ ±  3%   2.699µ ±  3%  -14.50% (p=0.000 n=10)
Slog/no_attrs-16           151.9n ± 13%   159.2n ± 17%        ~ (p=0.315 n=10)
Slog/3_attrs-16            225.2n ±  8%   230.2n ±  9%        ~ (p=0.280 n=10)
Slog/5_attrs-16            270.8n ± 27%   271.3n ± 15%        ~ (p=0.529 n=10)
Slog/10_attrs-16           1.446µ ± 11%   1.083µ ±  5%  -25.08% (p=0.000 n=10)
Slog/40_attrs-16           6.917µ ±  5%   5.902µ ± 10%  -14.67% (p=0.000 n=10)
Logr/no_attrs-16           9.234n ±  5%   8.139n ±  7%  -11.86% (p=0.000 n=10)
Logr/3_attrs-16            160.5n ±  5%   158.4n ±  3%        ~ (p=0.171 n=10)
Logr/5_attrs-16            247.4n ±  6%   259.1n ±  4%   +4.71% (p=0.045 n=10)
Logr/10_attrs-16          1135.0n ± 11%   998.6n ±  6%  -12.02% (p=0.000 n=10)
Logr/40_attrs-16           6.881µ ±  7%   5.554µ ±  6%  -19.29% (p=0.000 n=10)
geomean                    266.7n         233.3n        -12.52%

                        │    old.txt     │                new.txt                 │
                        │      B/op      │     B/op      vs base                  │
Emit/noop/no_attrs-16       0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Emit/noop/3_attrs-16        0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Emit/noop/5_attrs-16        0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Emit/noop/10_attrs-16       320.0 ± 0%       208.0 ± 0%  -35.00% (p=0.000 n=10)
Emit/noop/40_attrs-16     2.250Ki ± 0%     1.375Ki ± 0%  -38.89% (p=0.000 n=10)
Emit/writer/no_attrs-16     16.00 ± 0%       16.00 ± 0%        ~ (p=1.000 n=10) ¹
Emit/writer/3_attrs-16      48.00 ± 0%       48.00 ± 0%        ~ (p=1.000 n=10) ¹
Emit/writer/5_attrs-16      48.00 ± 0%       48.00 ± 0%        ~ (p=1.000 n=10) ¹
Emit/writer/10_attrs-16     408.0 ± 0%       296.0 ± 0%  -27.45% (p=0.000 n=10)
Emit/writer/40_attrs-16   2.570Ki ± 0%     1.695Ki ± 0%  -34.04% (p=0.000 n=10)
Slog/no_attrs-16            0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Slog/3_attrs-16             0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Slog/5_attrs-16             0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Slog/10_attrs-16           1168.0 ± 0%       816.0 ± 0%  -30.14% (p=0.000 n=10)
Slog/40_attrs-16          9.312Ki ± 0%     6.469Ki ± 0%  -30.54% (p=0.000 n=10)
Logr/no_attrs-16            0.000 ± 0%       0.000 ± 0%        ~ (p=1.000 n=10) ¹
Logr/3_attrs-16             128.0 ± 0%       128.0 ± 0%        ~ (p=1.000 n=10) ¹
Logr/5_attrs-16             208.0 ± 0%       208.0 ± 0%        ~ (p=1.000 n=10) ¹
Logr/10_attrs-16          1.344Ki ± 0%     1.000Ki ± 0%  -25.58% (p=0.000 n=10)
Logr/40_attrs-16          9.562Ki ± 0%     6.719Ki ± 0%  -29.74% (p=0.000 n=10)
geomean                                ²                 -14.07%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                        │   old.txt    │               new.txt               │
                        │  allocs/op   │ allocs/op   vs base                 │
Emit/noop/no_attrs-16     0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/noop/3_attrs-16      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/noop/5_attrs-16      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/noop/10_attrs-16     1.000 ± 0%     1.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/noop/40_attrs-16     1.000 ± 0%     1.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/writer/no_attrs-16   1.000 ± 0%     1.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/writer/3_attrs-16    4.000 ± 0%     4.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/writer/5_attrs-16    4.000 ± 0%     4.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/writer/10_attrs-16   8.000 ± 0%     8.000 ± 0%       ~ (p=1.000 n=10) ¹
Emit/writer/40_attrs-16   26.00 ± 0%     26.00 ± 0%       ~ (p=1.000 n=10) ¹
Slog/no_attrs-16          0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Slog/3_attrs-16           0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Slog/5_attrs-16           0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Slog/10_attrs-16          5.000 ± 0%     5.000 ± 0%       ~ (p=1.000 n=10) ¹
Slog/40_attrs-16          8.000 ± 0%     8.000 ± 0%       ~ (p=1.000 n=10) ¹
Logr/no_attrs-16          0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Logr/3_attrs-16           4.000 ± 0%     4.000 ± 0%       ~ (p=1.000 n=10) ¹
Logr/5_attrs-16           5.000 ± 0%     5.000 ± 0%       ~ (p=1.000 n=10) ¹
Logr/10_attrs-16          13.00 ± 0%     13.00 ± 0%       ~ (p=1.000 n=10) ¹
Logr/40_attrs-16          40.00 ± 0%     40.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean                              ²               +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean