feat: implment activity rules in controller

[siyuanfoundation]

closes: #867

This PR implements the following:

1. Implement activity probing via Jupyter API polling and pod exec scripts
2. Evaluate activity rules to determine when workspaces should be paused
3. Integrate with reconciliation to schedule probes and enforce culling decisions

Tested with tilt using JupyterLab WorkspaceKind.

1. verified eligibleAfter is properly populated, and the workspace is paused after being idle exceeding the secondsSinceActive
2. workspace is restarted and back running.
3. workspace is not paused if workspace stays active, and activity is resumed in time before the next probe.

[google-oss-prow]

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