buffer: create relative reading methods

[araujogui]

Introduces relative reading methods to Buffer, inspired by similar abstractions in Java and Rust's ByteBuffer. These methods maintain an internal reader index to support sequential reads without manually tracking offsets.

[araujogui]

Not sure how others feel about this — it adds a bit of complexity to Buffer, so before writing docs or going further, I'd like some feedback

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.23%. Comparing base (91d2400) to head (023d771).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #58295      +/-   ##
==========================================
+ Coverage   90.19%   90.23%   +0.03%     
==========================================
  Files         631      633       +2     
  Lines      186690   186979     +289     
  Branches    36665    36704      +39     
==========================================
+ Hits       168380   168713     +333     
+ Misses      11123    11071      -52     
- Partials     7187     7195       +8     

Files with missing lines	Coverage Δ
lib/internal/buffer.js	98.50% <100.00%> (-0.08%)	⬇️

... and 41 files with indirect coverage changes

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