IGNITE-27091 Fix client tx rollback to ignore connection errors

[ptupitsyn]

When the client disconnects, server rolls back the transaction automatically, so it does not make sense to throw IgniteClientConnectionException from rollback or rollbackAsync.

[Copilot]

Pull request overview

This PR addresses connection error handling during client transaction rollback operations. When a client disconnects or the server becomes unavailable, rollback operations now gracefully ignore connection exceptions instead of throwing errors, since the transaction is effectively rolled back on the server side when the connection is lost.

Changes:

• Modified client transaction rollback logic to catch and ignore IgniteClientConnectionException during rollback operations
• Added integration test to verify rollback behavior when client disconnects
• Added unit test to verify rollback behavior when server disconnects

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
ClientTransaction.java	Wrapped rollback logic to catch connection exceptions and return successfully, recognizing that disconnection implies server-side rollback
ItThinClientTransactionsTest.java	Added integration test verifying rollback succeeds after client disconnect for both sync and async cases
ClientTransactionsTest.java	Added unit test verifying rollback succeeds after server disconnect for both sync and async cases

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