Unsupported functions in protobuf serializatin

[alamb]

Describe the bug

Inspired by https://github.com/apache/arrow-datafusion/pull/8089/files from @Syleechan I checked if there were other functions not covered by our serialization logic. It turns out that yes there are:

To Reproduce

Remove the catchall in parse_expr:

diff --git a/datafusion/proto/src/logical_plan/from_proto.rs b/datafusion/proto/src/logical_plan/from_proto.rs
index cdb0fe9bda..52a8480146 100644
--- a/datafusion/proto/src/logical_plan/from_proto.rs
+++ b/datafusion/proto/src/logical_plan/from_proto.rs
@@ -1645,9 +1645,6 @@ pub fn parse_expr(
                 )),
                 ScalarFunction::Isnan => Ok(isnan(parse_expr(&args[0], registry)?)),
                 ScalarFunction::Iszero => Ok(iszero(parse_expr(&args[0], registry)?)),
-                _ => Err(proto_error(
-                    "Protobuf deserialization error: Unsupported scalar function",
-                )),
             }
         }
         ExprType::ScalarUdfExpr(protobuf::ScalarUdfExprNode { fun_name, args }) => {

The compiler will tell you there are several more functions not covered *like ToTimestamp and ArrowTypeOf:

error[E0004]: non-exhaustive patterns: `datafusion::ScalarFunction::ToTimestamp`, `datafusion::ScalarFunction::StructFun`, `datafusion::ScalarFunction::ArrowTypeof` and 2 more not covered
    --> datafusion/proto/src/logical_plan/from_proto.rs:1303:19
     |
1303 |             match scalar_function {
     |                   ^^^^^^^^^^^^^^^ patterns `datafusion::ScalarFunction::ToTimestamp`, `datafusion::ScalarFunction::StructFun`, `datafusion::ScalarFunction::ArrowTypeof` and 2 more not covered
     |
note: `datafusion::ScalarFunction` defined here

What this means is that if a user tries to serialize a plan with to_timestamp or arrow_typeof it will error with "Protobuf deserialization error"

Expected behavior

There should be no error

Additional context

No response

[alamb]

I think this is a good first issue as it has an example of how to fix it, and would get someone exposed to the various logical plan structures