serde integration, or custom proc macro for function arguments

Code like this is ugly, and similar code will exist in lots of places https://github.com/pydantic/monty/blob/3759c96394659e86c78c64126368b59752337e26/crates/monty/src/types/datetime.rs#L183 We should support parsing args/kwargs into a struct using `serde::Deserialize` if it can support all forms of arguments, or a custom procedural macro if it can't. So you would do something like ```rs #[derive(serde::Deserialize)] struct FunctionArgs { #[args_kwargs] a: i64, #[kwarg_only] b: String, } ```