refactor: Port TryCastExpr proto serialization hooks

[chakkk309]

Which issue does this PR close?

• Closes Port TryCastExpr to use try_to_proto / try_from_proto #22429.

Rationale for this change

This is part of #22418, which migrates built-in PhysicalExpr implementations away from the central protobuf serialization / deserialization chains.

TryCastExpr can now own its protobuf serialization through PhysicalExpr::try_to_proto and its deserialization through TryCastExpr::try_from_proto, matching the pattern used by previously migrated physical expressions.

What changes are included in this PR?

• Adds PhysicalExpr::try_to_proto support for TryCastExpr.
• Adds TryCastExpr::try_from_proto.
• Wires TryCastExpr deserialization in from_proto.rs through the new hook.
• Removes the old TryCastExpr serialization branch from the central to_proto.rs downcast chain.
• Adds direct proto hook tests for successful encoding / decoding and invalid protobuf inputs.

Are these changes tested?

Yes.

I ran:

cargo fmt --all --check
git diff --check
cargo test -p datafusion-physical-expr --features proto try_cast
cargo test -p datafusion-proto --test proto_integration
cargo clippy -p datafusion-physical-expr --features proto --tests -- -D warnings
cargo clippy -p datafusion-proto --tests -- -D warnings

Are there any user-facing changes?

No. This is an internal protobuf serialization refactor for TryCastExpr; the wire format remains unchanged.