chore: add Value depth level guard

[diegomarquezp]

• chore: add Value depth level guard
• chore: add tests

[gemini-code-assist]

Summary of Changes

Hello @diegomarquezp, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a crucial safeguard to the google::cloud::bigtable::Value class by implementing a recursion depth limit during type validation. This change addresses potential issues with excessively deep nested Value objects, such as arrays of arrays or deeply structured maps, which could lead to stack overflows or performance degradation. By capping the recursion at 10 levels, the system becomes more robust against malformed or overly complex data structures without impacting typical use cases.

Highlights

• Recursion Depth Guard: Implemented a depth limit of 10 levels for nested Value type validation to prevent stack overflows and excessive resource usage.
• Enhanced Type Matching Functions: Modified TypeAndValuesMatch and its recursive helpers (TypeAndArrayValuesMatch, TypeAndMapValuesMatch, TypeAndStructValuesMatch) to track and enforce the nesting depth.
• Comprehensive Testing: Added new test cases to value_test.cc specifically to verify the depth guard's functionality, ensuring that values exceeding the limit are correctly rejected and valid deeply nested values are accepted.

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[gemini-code-assist]

Code Review

This pull request introduces a depth guard to prevent stack overflows from deeply nested Value objects, which is a valuable defensive programming measure. The implementation correctly adds a depth parameter to the recursive validation functions and performs the necessary checks. Additionally, the tests have been improved to be more specific about error messages, and a new test case for the depth limit has been added. I have two suggestions for improvement: one to address duplicated code which violates the repository's style guide, and another to correct a confusing error message that appears to be a copy-paste error.

[codecov]

Codecov Report

❌ Patch coverage is 96.20253% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.94%. Comparing base (45fe5af) to head (a30afa5).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
google/cloud/bigtable/value.cc	88.88%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15778   +/-   ##
=======================================
  Coverage   92.94%   92.94%           
=======================================
  Files        2454     2454           
  Lines      226878   226919   +41     
=======================================
+ Hits       210879   210921   +42     
+ Misses      15999    15998    -1     

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