Recognize Laravel Macroable::mixin() registrations

[shuvroroy]

Summary

PHPantom already recovers Target::macro('name', $closure) registrations statically (and attaches facade macros to the concrete container-bound class). This PR extends the macro scanner to the other Macroable registration path: Target::mixin($object).

A mixin object's methods are closure factories — a public method foo() returns a Closure whose signature is the macro actually registered as Target::foo(...). We recover that shape from source without booting the app (Larastan boots and reflects the runtime $macros static; we parse the common literal form instead).

What it does

• Recognizes Target::mixin(new X) and Target::mixin(X::class), resolving X to an FQN via the file's use statements.
• For each public/protected method of X whose body returns a closure/arrow-fn, synthesizes a macro on Target named after the method, taking the returned closure's parameters and return type (mirroring Laravel's IS_PUBLIC | IS_PROTECTED; private/static/abstract/magic methods are skipped).
• Reuses the existing facade-target expansion, so a mixin registered through a facade also attaches to the facade's concrete class.
• Go-to-definition on a mixed-in macro jumps to the mixin method's own declaration.
• Editing the mixin class (e.g. adding a helper method) refreshes the recognized macros — the mixin source file is tracked as an index dependency even though it contains no macro(/mixin( token itself.

The result: mixin-contributed methods autocomplete, hover (with the recovered signature and a macro-origin marker), resolve, and type-check on the target class, exactly like a Target::macro(...) registration.

Scope / limitations

• Only literal new X / X::class arguments are handled; variable or computed targets are skipped, matching the existing macro() scope.
• Still out of scope for macro() too: variable/computed name arguments and string/array callables in place of a closure (rare, no statically recoverable signature).
• A mixin whose closures call methods on the rebound $this should carry an @mixin \Target docblock (the idiomatic Laravel pattern) so those $this->… calls resolve — this is handled by PHPantom's existing @mixin support, not this PR.

Testing

• Unit (macros_tests.rs): mixin-call extraction for both new X and X::class, skipping non-literal args and relative self:: targets, and closure-signature synthesis (including skipping methods that don't return a closure, and non-target classes in the same file).
• Integration (laravel_macros.rs): the mixin macro is surfaced in completion, resolves without diagnostics, go-to-definition lands on the mixin method, hover shows the recovered signature, and a $this-using mixin (with @mixin) resolves in completion + hover.
• cargo test, clippy (lib + tests), and cargo fmt --check are clean; analyze --project-root examples/laravel reports only pre-existing unrelated errors.

Example

Adds examples/laravel/app/Support/CollectionMixin.php registered via DemoServiceProvider::boot(), exercised in Demo.php.