fix: Reduce allocations for classic histogram buckets

[jaydeluca]

Related to #2075

This reduces allocation and GC pressure in histogram text formatting by eliminating unnecessary intermediate allocations.

[Copilot]

Pull request overview

This PR targets allocation reduction in the text exposition layer by removing repeated string building in hot formatting paths and replacing Long.toString(...) calls with direct writer-based long formatting. It also adds benchmark coverage around histogram text rendering so the impact can be measured in the benchmarking module.

Changes:

• Added a manual writeLong(...) helper in TextFormatUtil and reused it for counts and timestamps.
• Cached base/suffixed metric names in the Prometheus, OpenMetrics, and OpenMetrics 2 text writers to avoid repeated concatenation in loops.
• Added a histogram text-format JMH benchmark and updated benchmark tasks to run with the GC profiler.

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
prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/TextFormatUtil.java	Replaces Long.toString(...) with manual long/timestamp writing helpers.
prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/PrometheusTextFormatWriter.java	Caches metric names and suffixed variants to reduce per-datapoint allocations in Prometheus text output.
prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetricsTextFormatWriter.java	Applies the same cached-name optimization to OpenMetrics 1 text output.
prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriter.java	Reduces classic histogram bucket-name concatenation in OpenMetrics 2 text output.
mise.toml	Updates benchmark tasks to pass JMH GC-profiler arguments.
benchmarks/src/main/java/io/prometheus/metrics/benchmarks/HistogramTextFormatBenchmark.java	Adds a dedicated JMH benchmark for classic histogram text rendering.

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