MDEV-35465 Async replication stops working on Galera async replica no…

[temeo]

…de when parallel replication is enabled

• The Jira issue number for this PR is: MDEV-35465

Description

Parallel slave failed to retry in retry_event_group() with error

WSREP: Parallel slave worker failed at wsrep_before_command() hook

Fix wsrep transaction cleanup/restart in retry_event_group() to properly clean up previous transaction by calling wsrep_after_statement(). Also move call to reset error after call to wsrep_after_statement() to make sure that it remains effective.

Add a MTR test galera_as_slave_parallel_retry to reproduce the error when the fix is not present.

Other issues which were detected when testing with sysbench:

Check if parallel slave is killed for retry before waiting for prior commits in THD::wsrep_parallel_slave_wait_for_prior_commit(). This is required with slave-parallel-mode=optimistic to avoid deadlock when a slave later in commit order manages to reach prepare phase before a lock conflict is detected.

Suppress wsrep applier specific warning for slave threads.

How can this PR be tested?

This PR contains a new test galera.galera_as_slave_parallel_retry which was used to reproduce the issue. The test must pass when the fix is present.

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

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