feat: add typed metric family descriptors

[zeitlinger]

Adds typed metric family descriptors and typed metadata support for the model snapshots.

This is the typed-descriptor branch for downstreams that want to provide registration-time metadata explicitly. The #1800 Collector/MultiCollector registration metadata hooks are already optional via default methods, so unmodified downstreams should not need this PR just to keep working.

This PR now also deprecates the fragmented registration metadata API (getPrometheusName(), getMetricType(), getLabelNames(), and getMetadata() plus the MultiCollector variants) in favor of getMetricFamilyDescriptor() / getMetricFamilyDescriptors(). The deprecated methods remain bridged by default implementations for compatibility.

Related validation:

• test: validate Micrometer vanilla compatibility #2121 validates unmodified Micrometer independently of feat: add typed metric family descriptors #2114, against main + fix: restore reserved suffix stripping in PrometheusNaming.sanitizeMetricName() #2124.
• test: validate Micrometer opt-in compatibility #2123 validates a Micrometer branch that explicitly uses MetricFamilyDescriptor to implement the existing registration metadata hooks without invoking scrape/sample callbacks during registration.

[zeitlinger]

Opened draft validation PR #2121 to run the combined compatibility stack: opt-in typed descriptors, #2094 suffix sanitization, and the Micrometer compatibility workflow. This is intended as a proof/test PR so #2114 can stay focused.

[zeitlinger]

Opened #2122 as the smaller alternative implementation for #2114: same typed descriptor API, but legacy snapshot builders remain on plain metadata so the new descriptor behavior is opt-in. #2121 remains the combined validation PR with #2094 + Micrometer compatibility.

[zeitlinger]

Opened #2122 as the smaller alternative implementation for #2114: same typed descriptor API, but legacy snapshot builders remain on plain metadata so the new descriptor behavior is opt-in. #2121 remains the combined validation PR with #2094 + Micrometer compatibility.

closed that