Add naughty list for git remotes with persistent SSL/DNS errors

Implement domain-level naughty list tracking for git remotes, reusing the
existing NaughtyListTracker from relay sync. This prevents repeated attempts
to fetch from git domains with persistent infrastructure issues (SSL/TLS
certificate errors, DNS failures).

Changes:
- Updated NaughtyListTracker to track both relay URLs and git domains
- Added git_naughty_list field to RealSyncContext for error classification
- Modified fetch_oids() to classify git fetch errors and record naughty domains
- Updated sync_identifier_next_url() to filter out naughty domains during URL selection
- Added git_naughty_list parameter to ThrottleManager for domain queue processing
- Threaded naughty list through start_sync_loop and all sync functions
- Updated all tests to pass naughty list parameter

The naughty list uses 12-hour expiration (configurable) to allow domains to
recover from infrastructure issues. First occurrence logs WARN, repeats log DEBUG.

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