simplify function binding magic as an IntoFunction trait

[duncanawoods]

I believe most of the Callable/Handler structs/traits in magic.rs are not doing anything useful. If I am wrong, I will be curious to learn why!

This PR replaces them with a simpler IntoFunction trait which is much less weird and enables calling the boxed closure to without any unnecessary allocation.

[Copilot]

Pull Request Overview

This PR simplifies function binding in the interpreter by replacing the old Callable/Handler mechanism with a leaner IntoFunction trait that avoids unnecessary allocations.

• Replaces function call invocations in objects.rs from an indirect call method to a direct closure call.
• Removes legacy Handler/Callable types and updates the function registry in magic.rs.
• Adjusts macros and context retrieval in macros.rs and context.rs to support the new trait.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
interpreter/src/objects.rs	Updates function invocations and registry get method.
interpreter/src/magic.rs	Removes legacy function structures and defines the new IntoFunction.
interpreter/src/macros.rs	Revises macro implementations to implement IntoFunction.
interpreter/src/context.rs	Updates imports and changes get_function return type accordingly.

Comments suppressed due to low confidence (2)

interpreter/src/macros.rs:66

• [nitpick] Consider renaming the lambda parameter '_ftx' in the generated closures to a more descriptive name such as 'ctx' to improve readability.

impl<F, $($t,)* R> IntoFunction<($($t,)*)> for F

interpreter/src/context.rs:108

• Changing the return type from Option<Box> to Option<&Function> may affect consumers that expect an owned instance; please verify that all call sites can work with a borrowed Function.

pub(crate) fn get_function<S>(&self, name: S) -> Option<&Function>

[clarkmcc]

Thanks for this! That doesn't surprise me, I ripped a lot of the magic off of axum's implementation back in the day. It was due for a tidy!