Remove dead Admin#finalizer, fix cascading admin spec failures

[mensfeld]

Summary

• Remove dead Admin#finalizer instance method that captures self and could never work as a GC finalizer (same cleanup as Register Rdkafka::Consumer finalizer #841 did for Consumer)
• Fix cascading test failures in admin specs by replacing the after block with around/ensure — leaked handles are now cleared from the registry after each test, so a single timeout or broker error no longer poisons all subsequent tests
• Update CHANGELOG with Register Rdkafka::Consumer finalizer #841 attribution (jturkel)

Context

PR #841 (merged) fixed the missing Consumer finalizer registration and removed the dead Consumer#finalizer method. Admin had the same dead method.

The cascading test failure was discovered during CI for #841: with random seed 6333, a single admin test failure left a handle in the shared REGISTRY, causing the after block's expect(REGISTRY).to be_empty to fail on every subsequent test. The around/ensure pattern checks for leaks but always clears the registry, isolating failures.

Test plan

• CI passes with default random seed
• Verify the cascading failure is fixed (seed 6333 should no longer cascade)

[Copilot]

Pull request overview

This PR removes an unused Rdkafka::Admin#finalizer method and hardens the admin spec cleanup so a single leaking handle can’t cause cascading failures across subsequent examples.

Changes:

• Replace after cleanup assertions with an around/ensure that always clears leaked admin handle registries between examples.
• Remove dead Admin#finalizer method (finalization is handled via NativeKafka#finalizer).
• Add an Unreleased 0.25.3 section to the CHANGELOG documenting these fixes (and #841’s consumer finalizer work attribution).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
spec/lib/rdkafka/admin_spec.rb	Switch to around/ensure leak checking and forced registry cleanup to prevent cascading spec failures.
lib/rdkafka/admin.rb	Remove dead #finalizer instance method.
CHANGELOG.md	Add 0.25.3 (Unreleased) entries covering the finalizer cleanup and spec isolation fix.

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[Copilot]

All these handle classes appear to share the same REGISTRY constant via inheritance from Rdkafka::AbstractHandle (none of the admin handle subclasses define their own REGISTRY). As a result, registry_leaks will either be empty or contain all listed classes, and the failure message will be misleading about which handle type actually leaked. Consider checking/clearing Rdkafka::AbstractHandle::REGISTRY once and deriving leaked types from REGISTRY.values.map(&:class).uniq (or alternatively defining per-handle REGISTRY constants if separation is intended).

Suggested change

	registry_leaks = [
	Rdkafka::Admin::CreateTopicHandle,
	Rdkafka::Admin::CreatePartitionsHandle,
	Rdkafka::Admin::DescribeAclHandle,
	Rdkafka::Admin::CreateAclHandle,
	Rdkafka::Admin::DeleteAclHandle,
	Rdkafka::Admin::ListOffsetsHandle
	].reject { |handle_class| handle_class::REGISTRY.empty? }
	registry_leaks.each { |handle_class| handle_class::REGISTRY.clear }
	admin.close
	expect(registry_leaks).to be_empty, "Leaked handles in: #{registry_leaks.map(&:name).join(", ")}"
	admin_handle_classes = [
	Rdkafka::Admin::CreateTopicHandle,
	Rdkafka::Admin::CreatePartitionsHandle,
	Rdkafka::Admin::DescribeAclHandle,
	Rdkafka::Admin::CreateAclHandle,
	Rdkafka::Admin::DeleteAclHandle,
	Rdkafka::Admin::ListOffsetsHandle
	]
	registry = Rdkafka::AbstractHandle::REGISTRY
	leaked_handle_classes =
	registry.values.map(&:class).uniq & admin_handle_classes
	registry.clear
	admin.close
	expect(leaked_handle_classes).to be_empty,
	"Leaked handles in: #{leaked_handle_classes.map(&:name).join(", ")}"