keyv - feat: clean up of code with fixes and helpers

[jaredwray]

Please check if the PR fulfills these requirements

• Followed the Contributing and Code of Conduct guidelines.
• Tests for the changes have been added (for bug fixes/features) with 100% code coverage.

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
keyv - feat: clean up of code with fixes and helpers

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (12d728b) to head (63d766b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #1910      +/-   ##
===========================================
+ Coverage   99.88%   100.00%   +0.11%     
===========================================
  Files          37        38       +1     
  Lines        3409      3450      +41     
  Branches      526       531       +5     
===========================================
+ Hits         3405      3450      +45     
+ Misses          4         0       -4     

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[gemini-code-assist]

Code Review

This pull request refactors the core Keyv implementation by moving the main Keyv class from index.ts to a dedicated keyv.ts file and updating internal imports. The review feedback identifies several opportunities to improve the robustness and performance of the refactored code. Key suggestions include handling Promise.allSettled results more safely by checking fulfillment status instead of using unsafe type assertions, replacing non-idiomatic for...in array iteration with for...of, and optimizing the hasMany method by executing checks in parallel using Promise.all instead of sequential awaits.