fix(go): return error instead of panic on S2 decode failure

[atharvalade]

Which issue does this PR close?

Closes #3129

Rationale

Library code should never panic on bad server data — a truncated or corrupt S2-compressed message currently crashes the entire Go client process.

What changed?

DeserializeFetchMessagesResponse called panic() when s2.Decode failed on a malformed compressed payload. Callers had no way to recover.

Replaced panic(...) with return nil, fmt.Errorf(...) so the error propagates through the existing error return value. Added unit tests covering the malformed S2 path, the no-compression path, and the empty-payload path.

Local Execution

• Passed
• Pre-commit hooks ran (license-headers, trailing-whitespace, trailing-newline all clean on changed files)

AI Usage

1. Opus 4.6
2. Guided the fix and test scaffolding
3. Ran go test, go vet, and CI lint scripts locally; all pass
4. Yes, all code can be explained

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.80%. Comparing base (611fca0) to head (8577519).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3166      +/-   ##
============================================
- Coverage     74.10%   72.80%   -1.30%     
  Complexity      943      943              
============================================
  Files          1159     1117      -42     
  Lines        102033    96111    -5922     
  Branches      79083    73289    -5794     
============================================
- Hits          75607    69976    -5631     
+ Misses        23765    23591     -174     
+ Partials       2661     2544     -117     

Components	Coverage Δ
Rust Core	73.54% <ø> (-1.79%)	⬇️
Java SDK	62.30% <ø> (+2.15%)	⬆️
C# SDK	69.42% <ø> (+0.04%)	⬆️
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (ø)
Go SDK	39.63% <100.00%> (+0.20%)	⬆️

Files with missing lines	Coverage Δ
...nary_serialization/binary_response_deserializer.go	86.02% <100.00%> (+2.45%)	⬆️

... and 101 files with indirect coverage changes

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[chengxilo]

nit

Suggested change

	return nil, fmt.Errorf("iggy: failed to decode s2 payload: %w", err)
	return nil, fmt.Errorf("failed to decode s2 payload: %w", err)

[chengxilo]

LGTM