Create a binding generator trait

[e-nomem]

The goal is to deduplicate the code building the archive and adding type stubs, etc. This PR only adds the base trait and implements it for the PyO3 bindings. Once this PR looks good, I'll migrate the other bindings one at a time in separate PRs.

[Copilot]

Pull request overview

This PR introduces a BindingGenerator trait to deduplicate code for building archives and managing type stubs across different binding types. Currently, only PyO3 bindings are migrated to use this new trait, with other binding types (CFFI, UniFfi, WASM) to follow in separate PRs.

Key changes:

• Introduced BindingGenerator trait and GeneratorOutput struct to standardize binding generation interface
• Refactored PyO3 binding generation from a standalone function into a trait-based implementation (Pyo3BindingGenerator)
• Centralized common logic (Python part installation, artifact copying, type stub handling) into generate_binding() function

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/binding_generator/mod.rs	Added BindingGenerator trait, GeneratorOutput struct, and central generate_binding() function that handles the common workflow of installing Python files, artifacts, and type stubs
src/binding_generator/pyo3_binding.rs	Refactored from function-based to trait-based implementation; Pyo3BindingGenerator now implements BindingGenerator trait and focuses on PyO3-specific logic (filename generation, AIX archive handling, __init__.py generation)
src/build_context.rs	Updated to use new Pyo3BindingGenerator and generate_binding() instead of deprecated write_bindings_module() function
src/module_writer/path_writer.rs	Added #[cfg(target_family = "unix")] guard to default_permission import to match its Unix-only usage

[Copilot]

[nitpick] A temporary directory is now created for every build, even when not needed (only AIX builds require it for unpacking big archives). Consider creating it lazily or making it optional to avoid unnecessary filesystem operations for most builds.

Suggested change

	let temp_dir = tempdir()?;
	let GeneratorOutput {
	artifact_target,
	artifact_source_override,
	additional_files,
	} = generator.generate_bindings(context, interpreter, artifact, &module, &temp_dir)?;
	// Only create a temporary directory for AIX builds, as required.
	#[allow(unused_mut)]
	let mut temp_dir = None;
	let temp_dir_path = if cfg!(target_os = "aix") {
	temp_dir = Some(tempdir()?);
	temp_dir.as_ref().unwrap().path()
	} else {
	Path::new("")
	};
	let GeneratorOutput {
	artifact_target,
	artifact_source_override,
	additional_files,
	} = generator.generate_bindings(context, interpreter, artifact, &module, temp_dir_path)?;

[Copilot]

The BindingGenerator trait lacks documentation. Consider adding a doc comment that explains its purpose, when it should be implemented, and what each method parameter represents.