HHH-20783 Add a dedicated failed-transactions counter to Statistics

[pjs7678]

https://hibernate.atlassian.net/browse/HHH-20783

The failed-transactions value exposed by hibernate-micrometer as hibernate.transactions{result="failure"} was derived as
getTransactionCount() - getSuccessfulTransactionCount(). Since endTransaction() increments the two counters non-atomically, a concurrent reader (e.g. a Prometheus scrape) could transiently observe a negative value - and Micrometer 1.14+ (Prometheus Java client 1.x) rejects negative counters, failing the entire /actuator/prometheus scrape with HTTP 500.

As suggested by Christian Beikov on the forum (https://discourse.hibernate.org/t/12391), this introduces a dedicated counter:

• Statistics#getFailedTransactionCount() - new default method (derived fallback for custom implementations)
• StatisticsImpl - a dedicated LongAdder, incremented in endTransaction(false), reset in clear()
• HibernateMetrics now reads the dedicated counter, so the exposed value is exact, monotonic, and can never go negative (no transient overcount either, which could otherwise trip alerts on the failure counter)

Includes a regression test (deterministic success/rollback/clear cases plus a short concurrency guard). A standalone reproducer against the old derivation is attached to the Jira ticket (observes ~31k negative reads within 10 seconds on 6.6.55.Final).

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Please make sure that the following tasks are completed:
Tasks specific to HHH-20783 (Bug):

• Add test reproducing the bug
• Add entries as relevant to migration-guide.adoc OR check there are no breaking changes

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[beikov]

Please add a section to Statistics.adoc that is similar to the one for getSuccessfulTransactionCount(). As for the test, it's IMO fine to just add asserts to CMTTest and StatelessSessionStatisticsTest analogous to what has been done for getSuccessfulTransactionCount()

[pjs7678]

Thanks! Both addressed: documented getFailedTransactionCount in Statistics.adoc, and replaced the standalone test with asserts in CMTTest and StatelessSessionStatisticsTest.

[gavinking]

LGTM

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
80.0% Coverage on New Code
0.0% Duplication on New Code

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