GeezerVison

What this PR does / why we need it

Fixes #6660.

DynamoDBOnlineStore doesn't override OnlineStore.plan(), so it inherits the no-op default and feast plan never reports any DynamoDB table changes. SqliteOnlineStore and MilvusOnlineStore already implement plan(); this brings DynamoDB in line.

Adds:

• DynamoDBTable(InfraObject), using the InfraObject proto's CustomInfra field (protos/feast/core/InfraObject.proto), which exists specifically so online stores can add InfraObject support without a core proto change -- no other in-tree store uses it yet.
• DynamoDBOnlineStore.plan(), returning one DynamoDBTable per feature view (batch and stream).

Uses the corrected per-list pattern from #6659 (FeatureView.from_proto() for feature_views, StreamFeatureView.from_proto() for stream_feature_views) rather than applying one function to both, which is what caused the bug in #6658.

Scope note: this only changes what feast plan reports. feast apply's diff-based path (FeatureStore._should_use_plan(), which would call InfraObject.update()/teardown()) is gated to the local/sqlite provider only today, so DynamoDBOnlineStore.update()/teardown() -- which already perform the real table creation/deletion -- are completely unaffected. feast apply behavior for DynamoDB does not change.

Which issue(s) this PR fixes

Fixes #6660

Does this PR introduce a user-facing change?

`feast plan` now reports DynamoDB table changes instead of always showing none.

Test plan

• Added sdk/python/tests/unit/infra/online_store/test_dynamodb_plan.py: one table per feature view, stream feature views included (regression guard for the sqlite.py's OnlineStore.plan() raises typeguard.TypeCheckError for stream feature views #6658 bug pattern), batch + stream together, empty registry, and a full Infra proto round-trip through the CustomInfra/dotted-class-type path.
• Confirmed the new tests fail with the expected ImportError before this change, pass after.
• Ran the full sdk/python/tests/unit/infra/online_store/ directory (210 tests) -- no regressions.
• ruff check and ruff format --check pass on the changed files.