feat: treat all number types as field candidates

[waynexia]

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What's changed and what's your intention?

Queries like count(count(metric)) would generate a result in non-float64 type. In strict Prometheus Compatible mode (via Prometheus HTTP API) this would turn into an error. This patch adds a cast logic to extend the possible field types.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.85%. Comparing base (c93b76a) to head (1aacdd8).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3670      +/-   ##
==========================================
- Coverage   85.13%   84.85%   -0.29%     
==========================================
  Files         943      949       +6     
  Lines      157092   158558    +1466     
==========================================
+ Hits       133746   134542     +796     
- Misses      23346    24016     +670     

[killme2008]

LGTM