The cache key of `_get_server_keys_json` is a single argument which is
itself a `(server_name, key_id)` tuple, and `store_server_keys_response`
passed that nested tuple straight into the cache invalidation stream.
psycopg2 quietly serialises the inner tuple as a Postgres *record*, so
the `keys` column of `cache_invalidation_stream_by_instance` ended up
holding the record literal as a single string (e.g.
`{"(srv,ed25519:abc)"}`) — which never matches the real cache key on the
receiving side, i.e. the
invalidation has always been a silent no-op on workers. The native Rust
backend's stricter parameter conversion turns the same nested tuple into
a loud `TypeError: unsupported parameter type for postgres: tuple`.
Fix it the same way https://github.com/element-hq/synapse/pull/18899 did
for `_get_e2e_cross_signing_signatures_for_device`, which has the same
nested-tuple key shape: invalidate the local cache directly, JSON-encode
the key for the replication row, and decode it again in
`process_replication_rows`.
Found as part of the the effort to port the database pool to Rust.
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
