docs(humafiber): note streamed request bodies are not decoded

[wolveix]

Closes #1111.

With StreamRequestBody enabled, humafiber passes the raw BodyStream() through, so Content-Encoding isn't decoded. Buffered bodies still go through Fiber's Body() and arrive decoded (#928, #1058).

This documents that behaviour rather than decoding in the adapter:

• None of the other adapters decode request bodies (net/http never does), so the streaming path already matches them.
• Decoding ourselves means Fiber-only decompression with its own bomb protection (e.g. zstd window limits) and client error mapping. MaxBodyBytes alone doesn't cover it.
• Falling back to Body() when streaming isn't safe: fasthttp reads the whole stream into memory without enforcing the body limit.

Changes:

• Comment on BodyReader in both Fiber adapters explaining the passthrough.
• New "Compressed Request Bodies" section in the request limits docs, pointing to router middleware (e.g. Echo's middleware.Decompress).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.19%. Comparing base (47f6975) to head (fe41dad).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1118   +/-   ##
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  Coverage   93.19%   93.19%           
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  Files          24       24           
  Lines        5008     5008           
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  Hits         4667     4667           
  Misses        273      273           
  Partials       68       68           

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