feat: add native linear token admission

[jbachorik]

Summary

• adds a package-private, no-cache/no-fallback native named-LTS admission seam
• returns structured profile, parsing, plan, and capture-coverage rejections
• factors legacy named-only LTS routing through the same admission logic
• verifies original group indexes, cache isolation, and concurrent matcher independence

Validation

• ./gradlew jacocoVerify build
• final implementation-plan validation and independent code review

Stacked on #114.

[Copilot]

Pull request overview

Adds a package-private “native named-only LTS admission” seam in RuntimeCompiler that can return either an admitted LinearTokenSequenceMatcher or a structured rejection reason, and introduces tests to validate cache isolation, rejection taxonomy, capture index behavior, and matcher independence (including concurrency).

Changes:

• Introduced NamedOnlyLtsRejection + NamedOnlyLtsCompilation and tryCompileNamedOnlyLinearTokenSequence(...) to return structured admission results without touching legacy caches.
• Refactored the existing named-only LTS routing to share a single admission implementation (admitNamedOnlyLinearTokenSequence).
• Added NamedOnlyLtsAdmissionTest to cover admissions, rejections, capture projection/index preservation, and concurrency behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/RuntimeCompiler.java	Adds structured named-only LTS admission API and refactors admission logic to share the same implementation path.
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/NamedOnlyLtsAdmissionTest.java	Adds coverage for cache isolation, rejection reasons, matcher independence, and capture-index preservation.

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Codecov Report

❌ Patch coverage is 86.95652% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.4%. Comparing base (f4bb496) to head (362ae27).

Files with missing lines	Patch %	Lines
.../com/datadoghq/reggie/runtime/RuntimeCompiler.java	86.9%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@ Coverage Diff @@## agent/logs-reggie-l1d #115 +/- ##
=======================================================
Coverage 84.4% 84.4% Complexity 1 1 =======================================================
Files 147 147 Lines 43067 43087 +20 Branches 5890 5891 +1 =======================================================
+ Hits 36367 36394 +27 - Misses 4905 4906 +1 + Partials 1795 1787 -8 

Files with missing lines	Coverage Δ
.../com/datadoghq/reggie/runtime/RuntimeCompiler.java	87.8% <86.9%> (+0.8%)	⬆️

... and 3 files with indirect coverage changes

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