[beekld]

Summary

The FDv2 synchronizer loop measured its deadlines against the wall clock. When the system clock stepped backwards, every pending deadline was delayed by the size of the step. If every synchronizer was parked for 5 minutes and the clock stepped back an hour, no synchronizer ran for 65 minutes.

These deadlines now use MonotonicTime, a small value class over System.nanoTime(), so changes to the system clock don't move them.

Stacked on #252.

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Note

Overview
What changes

FDv2 synchronizer deadlines (recovery, fallback, wake scheduling), FDv1 fallback end times, and synchronizer park/unpark times now use a new MonotonicTime type backed by System.nanoTime(), so system clock adjustments no longer stretch or shrink those waits.

awaitUntil, earliest, and buildNextAvailableSynchronizer idle waits use monotonic durations (until) instead of Duration.between(Instant.now(), …).

Adds MonotonicTime ( now, plus, isBefore with overflow-safe comparison, until ) and MonotonicTimeTest for nanosecond overflow edge cases.

Risk for reviewers: Verify all call sites that compared or stored these deadlines now consistently use MonotonicTime and that nothing still mixes Instant for the same logical deadlines.

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