Make LogRecord fields private and add getters for encapsulation

[lalitb]

Changes

The PR refactors the LogRecord struct by making all its fields crate-private for better abstraction. Public getter methods have been added to provide controlled access to the fields.

TBD - Will add changelog, if the changes are agreed.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[lalitb]

Returning &str would simplify the API, but want to preserve the ability for consumers(i.e., exporter) to optimize based on whether the target is a static string.

[utpilla]

I think we could favor simplicity of the API here and use &str as the return type. The current exporters that we have cannot utilize the static str reference to their benefit anyway.

Only exporters that would benefit from Cow<'static, str> would be the ones that hold these values in memory for some reason as they could then avoid the cost to clone a static str.

[utpilla]

Not a strong opinion here as it's mainly used by exporters and not end users. We can expect exporter authors to work with Cow<'static,str>.

[lalitb]

Not a strong opinion here as it's mainly used by exporters and not end users. We can expect exporter authors to work with Cow<'static,str>.

Yes, that's what I thought - keeping it for the custom export authors if they want to reap the benefit of static target. Existing exporter (in main and contrib repo) won't get the benefit as they serialize the data to be sent across.

[codecov]

Codecov Report

Attention: Patch coverage is 85.24590% with 9 lines in your changes missing coverage. Please review.

Project coverage is 79.5%. Comparing base (465fcc2) to head (4507e16).

Files with missing lines	Patch %	Lines
opentelemetry-stdout/src/logs/exporter.rs	0.0%	8 Missing ⚠️
opentelemetry-proto/src/transform/logs.rs	92.3%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2314   +/-   ##
=====================================
  Coverage   79.5%   79.5%           
=====================================
  Files        123     123           
  Lines      21258   21275   +17     
=====================================
+ Hits       16905   16924   +19     
+ Misses      4353    4351    -2     

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