Clean up transactions after metadata rollback failures

[bill-ph]

Summary

Relevant: #1023

Fix DuckLake rollback cleanup when rolling back the metadata catalog connection fails.

Before this change, failures during metadata rollback could interrupt cleanup and leave transaction state behind. This was especially visible with Postgres metadata catalogs when the metadata backend connection was terminated: DuckLake could fail while trying to rollback, skip connection reset/local file cleanup, and leave the transaction registered in the transaction manager.

This change:

• factors metadata rollback into RollbackAndResetConnection()
• always resets the metadata connection after a rollback attempt
• preserves rollback errors and reports them to the caller
• ensures local file cleanup and local change cleanup still run before reporting rollback failure
• ensures DuckLakeTransactionManager::RollbackTransaction() erases the transaction before rethrowing rollback errors

Tests

Added Postgres metadata catalog sqllogictests for:

• commit failure where metadata rollback also fails, asserting both the commit error and rollback error are surfaced
• explicit ROLLBACK after terminating the metadata backend, asserting the rollback error is surfaced and the attachment remains usable afterward
• cleanup of locally written parquet files after rollback failure

Ran:

• cmake --build build/release --target unittest
• ./build/release/test/unittest --test-config test/configs/postgres.json --test-dir ./ test/sql/transaction/postgres_metadata_rollback_error.test
• ./build/release/test/unittest --test-config test/configs/postgres.json --test-dir ./ test/sql/transaction/postgres_metadata_explicit_rollback_error.test
• ./build/release/test/unittest --test-dir ./ test/sql/transaction/transaction_conflict_cleanup.test

[bill-ph]

The CI failure seems unrelated, these are existing tests, and are passing in other archs, can you rerun the failed CI job, @pdet ?