fix(geneva uploader): Replace unwrap/expect with graceful error handling

[lalitb]

Fixes #471

Changes

1. User-Agent header creation

   • Fallback to static "(Unknown) RustGenevaClient/0.1" if formatting fails
   • Log error with error!

2. MD5 hash formatting

   • Silently ignore write! errors (writing to String never fails)

3. Hex encoding

   • Log error with error! and return zeros on buffer mismatch

4. UTF-8 conversion (otlp_encoder.rs:573, 587, 610, 668, 682)

   • Log error with error! and return empty string for trace/span IDs

5. Timestamp conversion (otlp_encoder.rs:787-806)

   • Log error with error! and fallback to Unix epoch

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.8%. Comparing base (b49f00e) to head (d3bed22).

Files with missing lines	Patch %	Lines
...eneva-uploader/src/payload_encoder/otlp_encoder.rs	53.8%	12 Missing ⚠️
...eneva/geneva-uploader/src/config_service/client.rs	42.8%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #485     +/-   ##
=======================================
- Coverage   53.8%   53.8%   -0.1%     
=======================================
  Files         71      71             
  Lines      11687   11707     +20     
=======================================
+ Hits        6299    6304      +5     
- Misses      5388    5403     +15     

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[Copilot]

Pull Request Overview

This PR improves error handling by replacing .unwrap() calls with more graceful error handling strategies throughout the encoder and config client code. The changes add proper error logging using the tracing::error! macro and provide fallback values to prevent panics in production.

• Replaced .unwrap() calls with .unwrap_or_else() or if let Err() patterns
• Added structured error logging with contextual information for debugging
• Provided sensible fallback values for error cases (empty strings, zeros, epoch timestamps, static headers)

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
otlp_encoder.rs	Replaced unwrap calls with error logging and fallbacks for string formatting, UTF-8 conversion, hex encoding, and timestamp conversion
client.rs	Added error handling for User-Agent header creation with fallback to static header

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