ci: add testcase report workflow

[snoopuppy582]

Summary

• Add a dedicated Testcase Report workflow for PRs that touch the Rust core or testcase data.
• Run cargo test test_by_testcase -- --nocapture and parse the total/passed/failed testcase counts.
• Write the report to the GitHub Actions summary, and update a sticky PR comment for same-repository PRs where the workflow token can write comments.

Related Issue

• Closes Github action 리포트 기능을 통한 테스트 결과 출력 #106

Tests

• cargo test test_by_testcase -- --nocapture
• actionlint .github/workflows/testcase-report.yml

Notes

• The workflow is intentionally separate from the publish workflow so the testcase report can stay focused and reviewable.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 7 files with indirect coverage changes

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[github-actions]

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