fix: Resolve write_to_offline_store feature view with a single registry lookup - #6696

What this does

FeatureStore.write_to_offline_store resolved the feature view with a try/except chain (sdk/python/feast/feature_store.py):

try:
    feature_view = self.get_stream_feature_view(...)
except FeatureViewNotFoundException:
    try:
        feature_view = self.get_feature_view(...)
    except FeatureViewNotFoundException:
        feature_view = self.get_label_view(...)

For a plain FeatureView — the common case — the first lookup can never succeed. It is issued, raises FeatureViewNotFoundException, and is discarded, and only then does the lookup that can succeed run. A LabelView pays two failed lookups before the third.

Every getter forwards allow_registry_cache as the registry's allow_cache. On a CachingRegistry the failed attempts come from the cached proto and cost little. On a RemoteRegistry each is a gRPC round-trip to the registry server (it keeps no client-side cache and forwards allow_cache to the server as a request field). This sits on a per-batch write path, so a backfill pays a guaranteed-miss registry RPC before the real one on every batch, and allow_registry_cache=True (the default) does not avoid it.

The fix

Resolve the feature view with a single registry.get_any_feature_view(name, project, allow_cache=...) lookup — the unified accessor added in #4235 for exactly the case where a caller holds only a name. It covers FeatureView, StreamFeatureView, OnDemandFeatureView, and LabelView, so it is a behaviour-preserving replacement for the chain while collapsing up to three registry lookups into one.

#4235 introduced get_any_feature_view to address this same three-getters asymmetry in BaseRegistry and was closed as completed, but this call site was never migrated — it still performed the try/except chain, and a third branch (get_label_view) has been added since.

Testing

Added test_write_to_offline_store_resolves_feature_view_with_single_lookup (sdk/python/tests/unit/test_unit_feature_store.py): it asserts exactly one get_any_feature_view call and that none of the legacy per-type getters fire. The test fails against master (the chain calls get_stream_feature_view, not get_any_feature_view) and passes with this change.

ruff check/ruff format clean on both files; mypy clean on feature_store.py.

Fixes #6671.