Use BufReader for PyFileLikeObject with 1MB buffer

[manzt]

Wraps PyFileLikeObject in BufReader with a 1MB buffer for BAM, BCF,
VCF, and BigWig readers. Avoids changing the behavior of new to
prevent baking in assumptions about buffering needs or sizes, preserving
flexibility for unbuffered use cases.

---

Follow-up to #68

We want to avoid setting up the buffer inside new because it bakes in an opinion about buffering, which might conflict with cases where readers are already buffered, and it removes flexibility for users to configure buffer sizes or avoid buffering entirely if our choices are undesirable for their use case.

[pkerpedjiev]

Works for me 👍

You have some unused imports. Doesn't look like they're the result of this PR but maybe they just appeared because I was recompiling these files?

warning: unused import: `Read`
 --> /Users/pete/projects/oxbow/oxbow/src/fastq.rs:6:36
  |
6 |     io::{self, BufRead, BufReader, Read},
  |                                    ^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused imports: `Read` and `Seek`
 --> /Users/pete/projects/oxbow/oxbow/src/gff.rs:2:35
  |
2 | use std::io::{BufRead, BufReader, Read, Seek};
  |                                   ^^^^  ^^^^

warning: unused import: `Seek`
 --> /Users/pete/projects/oxbow/oxbow/src/gtf.rs:2:35
  |
2 | use std::io::{BufRead, BufReader, Seek};
  |