ben-manes / caffeine / #5460

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Stop ClockPro double-counting coldTarget on failed promotion

When canPromote runs runHandHot and every hot page between handHot and
the candidate is marked, the loop ends with handHot at the trigger.
nextHandHot then walks past the cold trigger and calls
terminateTestPeriod on it; because the candidate is still marked, that
adds a second +1 to coldTarget on top of the +1 already applied at the
top of canPromote.

Clear the marked bit after the explicit +1 so terminateTestPeriod
counts -1 if it fires for the candidate in the same call. Net behavior
matches both the paper ("+1 once per test-period access") and the
reference C implementation, which leaves credits unchanged in this
failure path. ClockProSimplePolicy already takes the equivalent
precaution (clearing marked before canPromote).

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