tests(tools): add unit tests for astfmtgen tool

[anujagrawal380]

Description

This PR adds comprehensive test coverage for the astfmtgen tool, which is responsible for generating optimized AST formatting code.

Issue

• Fixes: Testing: Add unit tests for astfmtgen tool #19072

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[anujagrawal380]

@timvaillancourt PTAL

[mattlord]

@anujagrawal380 you have failing tests. You should make sure that all tests are passing before asking for reviews.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.95%. Comparing base (e48c2d5) to head (34fef00).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19073      +/-   ##
==========================================
+ Coverage   69.90%   69.95%   +0.04%     
==========================================
  Files        1612     1612              
  Lines      215796   215817      +21     
==========================================
+ Hits       150858   150968     +110     
+ Misses      64938    64849      -89     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.