bridges/otellogrus: add kvBuffer abstraction for field conversion

[Rahuljagwani]

Solves #5428

This PR introduces a kvBuffer type to otellogrus for more consistent and maintainable field conversion, following the pattern established in otelslog.

Took reference from:
https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/bridges/otelslog/handler.go#L379

[linux-foundation-easycla]

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• ✅ login: Rahuljagwani / name: Rahul Jagwani (1c52759)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.2%. Comparing base (0558924) to head (4645c93).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8516   +/-   ##
=====================================
  Coverage   82.1%   82.2%           
=====================================
  Files        179     179           
  Lines      13700   13704    +4     
=====================================
+ Hits       11254   11269   +15     
+ Misses      2044    2033   -11     
  Partials     402     402           

Files with missing lines	Coverage Δ
bridges/otellogrus/hook.go	97.8% <100.0%> (+<0.1%)	⬆️

... and 1 file with indirect coverage changes

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[MrAlias]

This doesn’t add any behavior or capability; it just wraps a simple slice append loop in a new type and likely adds an extra allocation. Unless there’s a real follow‑on use, I don’t see the value here.

[Rahuljagwani]

Hi @MrAlias, the issue mentions about the comment of using kvbuffer.

I introduced this helper anticipating reuse for attribute filtering / normalization similar to Link. If that’s premature, should we ignore for now and introduce it later?

or

Do i need to write filter rules, nil checks etc.?