fix(server): evict model-suffixed cache keys on auto-reload

[alireza-aminzadeh]

Description

nemoguardrails server --auto-reload never applied config edits on a running server. Two bugs:

1. Cache-key mismatch: _get_rails() stores instances as config_id:model_name (because GuardrailCheckRequest.model is required on /v1/checks), but the watchdog only deleted the bare config_id. Eviction was a silent no-op for real traffic. The events-history restore path had the same mismatch.
2. Docker bind-mount inotify can stop delivering events with no error. The existing 5s monitor loop now polls file mtimes and evicts stale configs, and it restarts the observer if that thread has died.

Eviction now matches every cache key that includes the changed config id (bare, :model suffix, and hyphen-joined multi-config keys) and stores events history under those same keys.

Related Issue(s)

• Fixes bug: server --auto-reload never picks up config changes on a running server #2263
• Issue assignee: unassigned (issue is still status: needs triage; happy to wait for assignment if maintainers prefer)

Verification

• uv run --locked pytest tests/server/test_auto_reload.py -q — 16 passed
• Focused unit tests cover model-suffixed eviction, events-history restore keys, single-config path mapping, mtime polling (edit and delete), and the watchdog handler

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