[WIP] Refactor parse.Run to use an event generator

[karlkfi]

Pull the timers out of parse.Run and into a new GenerateFunc, implemented by TimedEventProducer.Generate.

Motivation:

• This should make it easier to test parse.Run deterministicly without needing to write a time-based test framework.
• This should also make parse.Run look more like a Reconcile loop from controller-runtime, which paves the way for further refactoring.
• This is not an ideal solution yet, just a next step towards something that's easier to test and easier to change.

Dependencies:

• https://github.com/GoogleContainerTools/kpt-config-sync/pull/1299

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[karlkfi]

/retest

[karlkfi]

/retest

[karlkfi]

/retest

[google-oss-prow[bot]]

@karlkfi: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
kpt-config-sync-presubmit-e2e-multi-repo-test-group1	b142636b621df33898083baee75298ba088184b6	link	true	/test kpt-config-sync-presubmit-e2e-multi-repo-test-group1
kpt-config-sync-presubmit-e2e-multi-repo-test-group3	b142636b621df33898083baee75298ba088184b6	link	true	/test kpt-config-sync-presubmit-e2e-multi-repo-test-group3
kpt-config-sync-presubmit-e2e-multi-repo-test-group2	b142636b621df33898083baee75298ba088184b6	link	true	/test kpt-config-sync-presubmit-e2e-multi-repo-test-group2

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