Fix AdaptiveRetry to retry retriable Left errors when shouldPayFailureCost is false

[adamw]

When shouldPayFailureCost returns false for a retriable Left error, AdaptiveRetry was incorrectly stopping retries instead of continuing them. This meant that errors configured to not incur a failure cost would halt prematurely rather than retrying for free.

The fix changes the logic to return ScheduleStop.No when shouldPayFailureCost is false, ensuring that retriable errors continue to be retried without consuming tokens from the bucket.

Added a test case verifying that all retry attempts execute when shouldPayFailureCost returns false, confirming 1 initial attempt plus 5 configured retries are all performed.

Fixes #442.

Closes #442.

[adamw]

The failure is clear and consistent across both Java 21 and 24 matrix entries. Here's the summary:

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CI failure: ImmediateRetryTest — AdaptiveRetry does not skip failureCost on retriable Left

Both matrix jobs (Java 21 and Java 24) fail on the same test:

- should not pay failureCost if result E is going to be retried and shouldPayFailureCost returns false *** FAILED ***
  1 was not equal to 6 (ImmediateRetryTest.scala:229)

The assertion at line 229 expects the retry count to reach 6 (i.e., the operation retried the full number of times without being halted by failure cost), but got 1 — meaning AdaptiveRetry stopped after the first attempt. This confirms the bug the PR was added to fix: when shouldPayFailureCost returns false for a retriable Left result, the retry loop still terminates early instead of continuing. The fix hasn't landed yet — this is the failing test added intentionally to document the bug.