[fix][txn] Fix SnapshotSegmentAbortedTxnProcessorImpl thread safety issue

[nikam14]

Fixes #22116

Motivation

Fix SnapshotSegmentAbortedTxnProcessorImpl thread safety issue

Modifications

1. Added volatile keyword to unsealedtxnIds variable.
2. Same resource were accessed at same line , so modified it.
3. Added synchronized keyword for data consistency

Verifying this change

• Make sure that the change passes the CI checks.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[lhotari]

Thanks for the contribution @nikam14 .

Unfortunately fixing these issues isn't simple. This PR might be doing the right things, but without proper concurrency tests, it's hard to ensure that adding synchronized methods doesn't cause regressions such as dead-locks. The lack of tests isn't caused by this PR, but to get confidence for merging such PRs, it would have to be resolved.
Just viewing the code won't be a sufficient review.

[nikam14]

Thanks for the explanation @lhotari