feat(admin): add in-memory metrics collector foundation

[Ferryx349]

Description

This PR adds the Phase 2 foundation for live admin metrics. It includes an in-memory AdminMetricsCollector and snapshot type for relay activity tracking.

Related Issue

Fixes - #652

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 29a6550

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
nostream	Minor

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[coveralls]

Coverage is 67.138% — Ferryx349:ADMIN-CONSOLE-2-metrics into cameri:main. No base build found for cameri:main.