What this PR does / why we need it:

Problem

DaskOfflineStore.get_monitoring_max_timestamp wraps pq.read_table in except Exception: return None, and None means "this source has no data". So a file that exists but cannot be read, or a storage error while reading it, is reported the same way as an empty source.

The callers act on that:

• MonitoringService logs "No data found for feature view '%s', skipping" and skips the feature view, so an unreadable source looks like an empty one.
• The baseline and compute paths pass the result as max_event_timestamp to _save_computed_metrics and _compute_for_feature_view, so the metrics are saved with no max_event_timestamp when the read failed.

compute_monitoring_metrics in the same store reads the same file without a handler, so it raises for the same failure.

Reproduction

A real parquet file in a temp repo, on master:

file with two rows               -> 2026-09-30 12:00:00+00:00
path that was never written      -> None
file containing b"not a parquet" -> None
read_table raising OSError       -> None

Change

Only FileNotFoundError returns None, since a source nothing has been written to has no data to monitor. Any other error reaches the caller, where MonitoringService already catches it per feature view and logs "Failed to auto-compute metrics for feature view".

I checked that a missing local path raises FileNotFoundError from pq.read_table with pyarrow 25.0.1. pyarrow's remote filesystems report a missing path the same way, but I did not run this against S3 or GCS.

Verification

New tests/unit/infra/offline_stores/test_dask_monitoring_max_timestamp.py, 4 tests. On master the corrupt-file and storage-error tests fail (DID NOT RAISE), and the 2 controls pass, a readable file and a missing path. With the change all 4 pass.

tests/unit/monitoring and test_dask_non_entity.py give the same 10 failures with and without the change, all in tests that need optional backends I don't have installed (BigQuery and others). ruff check and ruff format --check are clean. mypy reports 3 errors in dask.py at lines 183, 184 and 363, the same 3 as on master.

Which issue(s) this PR fixes:

None filed. Same class of fix as #6918, which does this for Trino's query_monitoring_metrics.

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change