feat(volcengine): add samples, service tests, and improve coverage

[Blankll]

eat(volcengine): add samples, service tests, and improve coverage

• Add Volcengine sample YAML files for API gateway, bucket, function, and VPC configurations
• Add Volcengine service tests for deploy and destroy flows
• Add vefaasTypes unit tests achieving 100% branch coverage
• Improve branch coverage from 84.81% to 85% threshold by adding:
  • cosStateBackend: error path tests for write and delete operations
  • lockUtils: empty git email fallback test
  • tablestorePlanner: null definition fallback test
  • localStack utils: single file root entry test
  • scfStack deployer/destroyer: database and ES partial failure tests
• Add context.test.ts for getIacLocation directory search
• Update runtimeMapper and validators for Volcengine runtime support
• Update README with Volcengine provider status

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.82%. Comparing base (8daa32b) to head (96edb09).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   87.50%   87.82%   +0.32%     
==========================================
  Files         139      144       +5     
  Lines        7866     8602     +736     
  Branches     2018     2216     +198     
==========================================
+ Hits         6883     7555     +672     
- Misses        466      498      +32     
- Partials      517      549      +32     

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