Remove AppendFloat from go/mysql/format and add required tests

[beingnoble03]

Description

This PR removes AppendFloat from go/mysql/format.
This PR also adds required unit tests for go/mysql/format

Related Issue(s)

Fixes #14972
Fixes part of #14931

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]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7800699) 47.29% compared to head (457f8c7) 47.30%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14986   +/-   ##
=======================================
  Coverage   47.29%   47.30%           
=======================================
  Files        1139     1140    +1     
  Lines      238914   238925   +11     
=======================================
+ Hits       113004   113012    +8     
- Misses     117315   117319    +4     
+ Partials     8595     8594    -1     

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