fix: report remaining, not elapsed, time from LinearRateLimiter

[csviri]

RateLimiter.isLimited is documented to return the "minimal duration
until a permission could be acquired again", but LinearRateLimiter
returned the time elapsed since the current period started:

Duration.between(actualState.getLastRefreshTime(), LocalDateTime.now())

The two are inverted. Measured with a 1000ms refresh period:

moment                  reported    correct
right after limit hit      19ms     ~1000ms
800ms into the period     804ms      ~200ms

EventProcessor.handleRateLimitedSubmission feeds this value straight
into TimerEventSource.scheduleOnce, so a rate-limited resource is
rescheduled almost immediately after the limit is reached (floored at
MINIMAL_RATE_LIMIT_RESCHEDULE_DURATION), gets rate-limited again, and
repeats — producing a burst of pointless timer events. Conversely, a
resource limited near the end of a period waits roughly a full extra
period after a permission was already available.

Now returns the time until the current period ends, clamped at zero.

returnsMinimalDurationToAcquirePermission only asserted
isLessThan(REFRESH_PERIOD), which held for both the correct and the
inverted value; it now also asserts the reported wait is close to the
full period. A second test asserts the reported duration shrinks as the
period elapses, which is what distinguishes remaining from elapsed. Both
fail without this change.

Part of #3517

[Copilot]

Pull request overview

Fixes LinearRateLimiter#isLimited to report the remaining time until a permission can be acquired (as documented), preventing overly-early rescheduling of rate-limited resources.

Changes:

• Update LinearRateLimiter.isLimited to compute remaining time in the current refresh period (clamped at zero).
• Strengthen returnsMinimalDurationToAcquirePermission to assert the reported wait is close to the full refresh period.
• Add a regression test ensuring the reported duration decreases as the refresh period elapses.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/rate/LinearRateLimiter.java	Switches isLimited from reporting elapsed time to reporting remaining time in the refresh period.
operator-framework-core/src/test/java/io/javaoperatorsdk/operator/processing/event/rate/LinearRateLimiterTest.java	Updates and adds tests to distinguish “remaining” vs “elapsed” duration behavior.