feat: Add domain exceptions to skip or cancel test

[roxblnfk]

What was changed

Added domain exceptions to skip or cancel test

Checklist

• Tested
  • Unit tests added

[Copilot]

Pull request overview

Adds status-bearing domain exceptions so tests can explicitly end as skipped or cancelled, and documents the behavior for Testo users and plugin authors.

Changes:

• Adds SkipTest / CancelTest exceptions and maps them in TestRunner to Status::Skipped / Status::Cancelled.
• Adds feature coverage using a real runner and a stub suite.
• Updates Testo skills documentation and contributor guidance for the new public behavior.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
core/Core/Exception/SkipTest.php	Adds skip marker exception.
core/Core/Exception/CancelTest.php	Adds cancellation marker exception.
core/Application/Internal/Runner/TestRunner.php	Maps marker exceptions to non-error statuses.
core/Core/Context/CaseInfo.php	Renames test execution callback from invoker to handler.
core/Application/Internal/Runner/SuiteRunner.php	Updates CaseInfo construction for renamed callback.
tests/Application/suites.php	Adds Application feature test suite.
tests/Application/Stub/Runner/StatusFromException.php	Adds runner stub cases for exception status mapping.
tests/Application/Feature/Runner/StatusFromExceptionTest.php	Adds feature tests for skip/cancel/error mapping.
skills/testo-write-tests/SKILL.md	Documents skip/cancel usage in tests.
skills/testo-plugin-author/SKILL.md	Documents interceptor behavior for skip/cancel.
skills/testo-migrate-from-phpunit/SKILL.md	Adds PHPUnit migration guidance for skipped/incomplete tests.
skills/testo-flaky-tests/SKILL.md	Notes retry/repeat behavior with skip/cancel.
skills/README.md	Adds skills index and source-of-truth notes.
CLAUDE.md	Adds contributor guidance to update skills with public API changes.

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