fix: harden Buffer collection and stripe indexing

[arnabnandy7]

Summary

Fixes #2287 and #2282 in prometheus-metrics-core’s Buffer.

Changes

• Bound the Buffer.run() spin wait during collection so the buffer cannot stay active indefinitely while waiting for in-flight observations.
• On timeout, deactivate the buffer, replay already buffered observations, then throw an IllegalStateException.
• Preserve existing side-effect-only Buffer.run() callers that intentionally return null.
• Replace the stripe index calculation with Math.floorMod(threadId, stripeCount) to avoid Math.abs(Integer.MIN_VALUE) overflow.
• Add regression tests for both timeout cleanup behavior and the Integer.MIN_VALUE thread-id narrowing case.

Validation

• mise run lint:fix
• .\mvnw test -pl prometheus-metrics-core '-Dtest=BufferTest' '-Dcoverage.skip=true' '-Dcheckstyle.skip=true'
• .\mvnw test -pl prometheus-metrics-core '-Dtest=HistogramTest#testGolangTests,BufferTest' '-Dcoverage.skip=true' '-Dcheckstyle.skip=true'
• .\mvnw install -pl prometheus-metrics-core -am -DskipTests '-Dcoverage.skip=true'
• git diff --check

Note: mise run build does not run directly in this Windows shell because the task invokes Unix-style ./mvnw; the equivalent Maven wrapper commands above passed.