feat: user-agent header in gRPC

[karel-rehor]

Proposed Changes

• Sets user-agent header in metadata for query calls by default
• Adds test for default headers in query calls
• Cleans up a couple of lines in writer that linter complained about locally

Checklist

• [ ] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] A test has been added if appropriate
• [x] Tests pass
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.34%. Comparing base (d1bf97b) to head (c908413).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #85 +/- ## ========================================== - Coverage 83.38% 83.34% -0.04% ========================================== Files 12 12 Lines 1011 1009 -2 ========================================== - Hits 843 841 -2 Misses 138 138 Partials 30 30 ```

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