ci(go): merge BDD and e2e test coverage into Go SDK Codecov reports

[atharvalade]

Which issue does this PR close?

Closes #2858

Rationale

Go SDK coverage was only capturing unit tests from foreign/go/, missing all BDD integration tests (bdd/go/) and e2e tests that exercise the SDK through a running server. This artificially deflated the reported coverage.

What changed?

The post-merge go-coverage job and pre-merge e2e task only ran cd foreign/go && go test ./..., ignoring 49 BDD test files in bdd/go/ that exercise streams, topics, messaging, consumer groups, offsets, users, and more through the SDK.

Now both workflows also run bdd/go tests with -coverpkg=github.com/apache/iggy/foreign/go/... to capture SDK code coverage from integration tests, merge the profiles, and upload the combined result to Codecov. The _test.yml upload step now triggers on both test and e2e tasks, matching the Node SDK pattern.

Local Execution

• Passed
• Pre-commit hooks ran — no Go/Rust/Java code changed, only CI workflow YAML files

AI Usage

1. Opus 4.6
2. Used for codebase exploration, pattern analysis across SDK workflows, and generating the workflow YAML changes
3. Verified by cross-referencing with existing Node/C# coverage patterns in the same repo, validating YAML syntax, and checking file path consistency across all three modified files
4. Yes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.93%. Comparing base (ecd7709) to head (95d3b2e).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2859      +/-   ##
============================================
+ Coverage     68.36%   69.93%   +1.57%     
  Complexity      739      739              
============================================
  Files          1053     1053              
  Lines         84763    84763              
  Branches      61297    61307      +10     
============================================
+ Hits          57948    59283    +1335     
+ Misses        24448    22996    -1452     
- Partials       2367     2484     +117     

Flag	Coverage Δ
csharp	67.43% <ø> (-0.19%)	⬇️
go	36.31% <ø> (+30.04%)	⬆️
java	54.83% <ø> (ø)
node	92.26% <ø> (-0.15%)	⬇️
python	81.57% <ø> (ø)
rust	70.00% <ø> (-0.06%)	⬇️

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see 70 files with indirect coverage changes

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