evalengine: Implement PERIOD_DIFF

[beingnoble03]

Description

This PR adds implementation of PERIOD_DIFF func in evalengine. This PR borrows some changes related to period functions from #16492.

Related Issue(s)

• evalengine: Support all built-in MySQL functions #9647

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 89.23077% with 7 lines in your changes missing coverage. Please review.

Project coverage is 68.79%. Comparing base (0b7c0e4) to head (73e392f).
Report is 1 commits behind head on main.

Files	Patch %	Lines
go/vt/vtgate/evalengine/fn_time.go	90.90%	3 Missing ⚠️
go/vt/vtgate/evalengine/compiler_asm.go	86.66%	2 Missing ⚠️
go/vt/vtgate/evalengine/translate_builtin.go	66.66%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16557   +/-   ##
=======================================
  Coverage   68.78%   68.79%           
=======================================
  Files        1556     1556           
  Lines      199803   199868   +65     
=======================================
+ Hits       137429   137490   +61     
- Misses      62374    62378    +4     

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