Issue errors when checkstyle detects an violation in GitHub CI

[jjppp]

This PR configures checkstyle to issue errors instead of warnings when codeing-style violations are detected in GitHub CI, as in this CI run, and fixes a coding-style violation related to the license header of a test driver.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.78%. Comparing base (064801b) to head (084c152).

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #202   +/-   ##
=========================================
  Coverage     75.78%   75.78%           
  Complexity     4659     4659           
=========================================
  Files           481      481           
  Lines         16055    16055           
  Branches       2198     2198           
=========================================
  Hits          12167    12167           
+ Misses         3020     3019    -1     
- Partials        868      869    +1     

see 2 files with indirect coverage changes

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[zhangt2333]

Currently, the checkstyle warnings are not natively reported by checkstyle itself - I wrote a utility class to format and output them.

Tai-e/buildSrc/src/main/kotlin/checkstyle.conventions.gradle.kts

Line 20 in 064801b

doLast { summarizeStyleViolations(this as Checkstyle)?.let(logger::warn) }

In this PR, directly enabling checkstyle's option would actually suppress our style violation reporting.

My suggestion is that we have another approach to report style violations in PR comments, such as reviewdog.

[jjppp]

Will do this with a better tool such as review dog, closing.