break(framework): Delete FFS and use LinkState instead

[danieljanes]

Merge after #6809

This PR:

• Replaces all FFS usage with LinkState store_fab and get_fab
• Removes all FFS usage
• Deletes FFS (inc. all implementations)

[Copilot]

Pull request overview

This PR completes the migration away from the legacy Flower File Storage (FFS) by moving FAB persistence/retrieval fully onto LinkState/NodeState via store_fab/get_fab, and removes the FFS implementation and related CLI/configuration surface.

Changes:

• Replace FFS-based FAB storage/retrieval with state.store_fab(...) / state.get_fab(...) across SuperLink/SuperNode APIs.
• Remove FFS plumbing (factories, CLI flags, runtime wiring) and delete the flwr.supercore.ffs package.
• Update tests and documentation to reflect the breaking storage change (FABs stored in state rather than local ffs/).

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
framework/py/flwr/supernode/start_client_internal.py	Stop initializing/using FFS; store FABs via NodeState.store_fab.
framework/py/flwr/supernode/start_client_internal_test.py	Update unit tests to remove FFS mocks and assert store_fab calls.
framework/py/flwr/supernode/servicer/clientappio/clientappio_servicer.py	Replace FAB reads from FFS with NodeState.get_fab.
framework/py/flwr/supernode/servicer/clientappio/clientappio_servicer_test.py	Update servicer construction after removing ffs_factory dependency.
framework/py/flwr/superlink/servicer/control/control_servicer.py	Store FABs via LinkState.store_fab during StartRun.
framework/py/flwr/superlink/servicer/control/control_servicer_test.py	Remove tempfile/FFS setup; rely on state-backed FAB storage.
framework/py/flwr/superlink/servicer/control/control_grpc.py	Remove ffs_factory from Control API server wiring.
framework/py/flwr/supercore/ffs/ffs.py	Deleted: FFS abstract interface removed.
framework/py/flwr/supercore/ffs/ffs_test.py	Deleted: FFS conformance tests removed.
framework/py/flwr/supercore/ffs/ffs_factory.py	Deleted: FFS factory removed.
framework/py/flwr/supercore/ffs/ffs_factory_test.py	Deleted: FFS factory tests removed.
framework/py/flwr/supercore/ffs/disk_ffs.py	Deleted: disk-based FFS implementation removed.
framework/py/flwr/supercore/ffs/init.py	Deleted: FFS package exports removed.
framework/py/flwr/server/superlink/serverappio/serverappio_servicer.py	Replace FFS usage with LinkState.get_fab for ServerApp inputs.
framework/py/flwr/server/superlink/serverappio/serverappio_servicer_test.py	Update tests to store FABs via state.store_fab (hash-validated).
framework/py/flwr/server/superlink/serverappio/serverappio_grpc.py	Remove ffs_factory parameter from ServerAppIo gRPC server wiring.
framework/py/flwr/server/superlink/fleet/rest_rere/rest_api.py	Drop FFS dependency and route FAB retrieval through state/message handler.
framework/py/flwr/server/superlink/fleet/message_handler/message_handler.py	Update get_fab handler to read from state and validate hash matches run.
framework/py/flwr/server/superlink/fleet/grpc_rere/node_auth_server_interceptor_test.py	Update FAB setup to use state.store_fab and run FAB hash.
framework/py/flwr/server/superlink/fleet/grpc_rere/fleet_servicer.py	Remove ffs_factory dependency; call updated message_handler.get_fab.
framework/py/flwr/server/superlink/fleet/grpc_rere/fleet_servicer_test.py	Update tests to use state-backed FAB storage; add hash-mismatch rejection case.
framework/py/flwr/server/superlink/fleet/grpc_adapter/grpc_adapter_servicer_test.py	Update adapter servicer construction after FleetServicer signature change.
framework/py/flwr/server/app.py	Remove --storage-dir flag and all FFS initialization/wiring from SuperLink runtime.
framework/py/flwr/cli/local_superlink.py	Stop creating/passing an ffs/ directory to the managed local SuperLink process.
framework/py/flwr/cli/local_superlink_test.py	Adjust CLI spawn assertions to ensure --storage-dir is no longer used.
framework/docs/source/how-to-run-flower-locally.rst	Document breaking change: FABs stored in state, legacy ffs/ data not migrated.

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