PBM-1756: Adding e2e tests scenarios not already covered

[keithquinnpercona]

No description provided.

[Copilot]

Pull request overview

Adds multiple new PBM end-to-end scenarios (PITR, selective restore, agent interruptions, clock skew, distributed transactions) to expand functional coverage of backup/restore behavior across different cluster topologies, and introduces a small Cluster helper to support PITR-timestamp selection.

Changes:

• Added new e2e tests covering: unsharded timeseries PITR, selective restore, backup interruption/cancel behavior, leader/agent lag, distributed transactions, clock skew handling, and restore metadata cleanup.
• Updated incremental backup tests (replicaset + sharded) to run with continuous writes during incremental backup creation.
• Updated the pytest image to install libfaketime and added Cluster.get_last_pitr_chunk_end() to support PITR testing.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pbm-functional/pytest/test_timeseries.py	Adds an unsharded timeseries PITR test with concurrent writers and restore verification.
pbm-functional/pytest/test_sharded.py	Updates incremental test to run under continuous writes; adds “lost shard agent mid-backup” scenario; changes storage-config parametrization.
pbm-functional/pytest/test_selective_restore.py	New selective backup + selective restore coverage for replicaset and sharded layouts.
pbm-functional/pytest/test_replicaset.py	Updates incremental test to run under continuous writes and verify restore correctness.
pbm-functional/pytest/test_PBM-1344.py	Adds S3/MinIO validation that delete-backup removes remote artifacts.
pbm-functional/pytest/test_leader_lag.py	New test ensuring a paused CSRS agent can resume and complete a backup, then survives resync/restore.
pbm-functional/pytest/test_distributed_trx.py	New PITR + physical tests validating behavior with cross-shard distributed transactions.
pbm-functional/pytest/test_clockskew.py	New logical/physical tests for backup/restore correctness with per-shard clock skew via faketime.
pbm-functional/pytest/test_cleanup_restore.py	New test validating restore cleans up chunk routing metadata changes after snapshot.
pbm-functional/pytest/test_backup_interruption.py	New tests for cancel-backup cleanup and delete-backup behavior during an active backup.
pbm-functional/pytest/Dockerfile	Installs libfaketime to enable clock-skew testing.
pbm-functional/pytest/cluster.py	Adds helper to fetch the latest PITR chunk end timestamp.

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