feat(testing-sdk): add option to specify checkpoint delay on local runner

[anthonyting]

Issue #, if available:

Description of changes:

To help root cause #365 locally.

Adding a checkpointDelay option to LocalDurableTestRunner.setup. Example:

await LocalDurableTestRunner.setup({
  checkpointDelay: 100
})

To have integ tests pass, I have temporarily commented out the problematic assertions.

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