dynamic_modules: expose stat tags and tag-extracted names in the stats sink ABI

[basundhara-c]

Commit Message: expose stat tags and tag-extracted names in the stats sink ABI
Additional Description:

The stats sink ABI previously exposed only each stat's full, flat name (e.g. cluster.foo.upstream_rq_total) and its value. This adds callbacks to also read a stat's tag-extracted name and its tags (name/value pairs) for counters, gauges, etc.

This lets a custom dynamic-module stats sink consume the same dimensional decomposition Envoy's built-in formatters use so it can reconstruct labelled output like envoy_cluster_upstream_rq_total{cluster_name="foo"} instead of only the flat name.

Risk Level: Low
Testing: Tests Added
Docs Changes: N.A
Release Notes: N.A
Platform Specific Features: N.A

[repokitteh-read-only]

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🐱

Caused by: #46028 was opened by basundhara-c.

see: more, trace.

[basundhara-c]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces new ABI functions and Rust SDK wrappers to retrieve tag-extracted names, tag counts, and individual tags for counters, gauges, and text readouts in Envoy dynamic modules. It also refactors buffer-filling logic in the Rust SDK and adds comprehensive unit tests in both C++ and Rust. The feedback points out a minor documentation mismatch in the Rust SDK where counter_tag_extracted_name is documented as returning None instead of false when the index is out of range.

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[gemini-code-assist]

The doc comment for counter_tag_extracted_name states that it returns None when the index is out of range, but the function actually returns a bool (returning false on failure). The documentation should be updated to reflect the correct return type.

Suggested change

	/// values removed). Returns `None` and leaves `name` unchanged when the index is out of range.
	/// values removed). Returns false and leaves name unchanged when the index is out of range.