feat: add bounded native pattern cache

[jbachorik]

Summary

Adds an opt-in, bounded, instance-owned cache for native named-LTS compiled patterns.

• Successful native patterns are cached with exact LRU capacity.
• Rejections are never cached; legacy RuntimeCompiler caches remain untouched.
• Equal concurrent requests share in-flight admission; clear and exceptional admission behavior are deterministic and tested.

Validation

• ./gradlew :reggie-runtime:test --tests com.datadoghq.reggie.runtime.ReggieCompiledPatternCompilerTest
• ./gradlew :reggie-runtime:test
• ./gradlew spotlessApply
• final implementation-plan validation: clean
• final independent code review: clean

[Copilot]

Pull request overview

Adds an opt-in, bounded, instance-owned cache for native named linear-token-sequence (LTS) compiled patterns, including a configurable “maximum source length” budget gate and single-flight behavior for concurrent identical compile requests.

Changes:

• Introduces ReggieCompiledPatternCompiler with an exact-capacity LRU cache and in-flight deduplication using CompletableFuture.
• Adds ReggieNativeCompileBudget and a new rejection reason SOURCE_TOO_LONG for over-budget requests.
• Adds comprehensive unit tests covering LRU eviction/recency, cache independence, deterministic exceptional admissions, and budget boundary + concurrency behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompiledPatternCompiler.java	New bounded, instance-owned LRU cache + in-flight single-flight admission mechanism.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieNativeCompileBudget.java	New budget type for rejecting overly long sources prior to admission/in-flight registration.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompiledPattern.java	Refactors compilation entry to route through tryCompileNative helper used by the compiler.
reggie-runtime/src/main/java/com/datadoghq/reggie/runtime/ReggieCompilationRejection.java	Adds SOURCE_TOO_LONG rejection reason.
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/ReggieCompiledPatternCompilerTest.java	New tests for LRU behavior, independence, concurrency single-flight, clear-during-admission, and exceptional admissions.
reggie-runtime/src/test/java/com/datadoghq/reggie/runtime/ReggieNativeCompileBudgetTest.java	New tests for budget validation, UTF-16 length semantics, and concurrency behavior under budget rejection.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.41758% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.4%. Comparing base (f7b758a) to head (9d259b3).

Files with missing lines	Patch %	Lines
.../reggie/runtime/ReggieCompiledPatternCompiler.java	86.8%	7 Missing and 3 partials ⚠️
...atadoghq/reggie/runtime/ReggieCompiledPattern.java	40.0%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##             agent/logs-reggie-l1g    #118     +/-   ##
=========================================================
- Coverage                     84.4%   84.4%   -0.1%     
  Complexity                       1       1             
=========================================================
  Files                          153     155      +2     
  Lines                        43194   43283     +89     
  Branches                      5898    5910     +12     
=========================================================
+ Hits                         36498   36571     +73     
- Misses                        4906    4918     +12     
- Partials                      1790    1794      +4     

Files with missing lines	Coverage Δ
...ghq/reggie/runtime/ReggieCompilationRejection.java	100.0% <100.0%> (ø)
...oghq/reggie/runtime/ReggieNativeCompileBudget.java	100.0% <100.0%> (ø)
...atadoghq/reggie/runtime/ReggieCompiledPattern.java	70.0% <40.0%> (-30.0%)	⬇️
.../reggie/runtime/ReggieCompiledPatternCompiler.java	86.8% <86.8%> (ø)

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