Server start events

[EricGustin]

1. Refactored the core usage logic from arcade_cli to arcade_core
2. Add "MCP server started" event

As always, opt out by setting ARCADE_USAGE_TRACKING to 0.

[codecov]

Codecov Report

❌ Patch coverage is 75.25773% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...p-server/arcade_mcp_server/usage/server_tracker.py	48.88%	23 Missing ⚠️
...ibs/arcade-core/arcade_core/usage/usage_service.py	75.00%	1 Missing ⚠️

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