Support ser/de of AsyncFuncExec #19112

Is your feature request related to a problem or challenge?

Currently we cannot ser/de plans with AsyncFuncExec nodes:

Exception: DataFusion error: ArrowError(ExternalError(Execution("Job 2ldUC9Y failed: DataFusion error: Internal error: Unsupported plan and extension codec failed with [Internal error: unsupported plan type: AsyncFuncExec { async_exprs: [AsyncFuncExpr....

Describe the solution you'd like

• Add a proto definition for this physical plan node
• Support round-tripping it with a test

Describe alternatives you've considered

n/a

Additional context

n/a