Sub-issue of #22418. Port UnKnownColumn to use the try_to_proto / try_from_proto hooks added in #21929.
Replace the UnKnownColumn arm in datafusion/proto/src/physical_plan/{to_proto,from_proto}.rs with try_to_proto / try_from_proto impls next to UnKnownColumn. See the Column / BinaryExpr migrations in #21929 for reference.
Sub-issue of #22418. Port
UnKnownColumnto use thetry_to_proto/try_from_protohooks added in #21929.Replace the
UnKnownColumnarm indatafusion/proto/src/physical_plan/{to_proto,from_proto}.rswithtry_to_proto/try_from_protoimpls next toUnKnownColumn. See theColumn/BinaryExprmigrations in #21929 for reference.