Add vectorcall (PEP 590) dispatch for function calls by youknowone · Pull Request #7329 · RustPython/RustPython

* Add vectorcall (PEP 590) dispatch for function calls

Add VectorCallFunc slot to PyTypeSlots and vectorcall dispatch path
in the interpreter loop for Call and CallKw instructions.

Implement vectorcall for PyFunction (with fast path for simple
positional-only calls that fills fastlocals directly), PyBoundMethod
(avoids prepend_arg O(n) shift), and PyNativeFunction.

Add FuncArgs::from_vectorcall helper for fallback conversion.
Vectorcall slot is inherited with call slot and cleared when
__call__ is overridden in Python subclasses.

* Optimize vectorcall: move args instead of clone, use vectorcall in specialized paths

- invoke_exact_args takes Vec by value and uses drain() to move args
  into fastlocals instead of cloning (eliminates refcount overhead)
- CallPyGeneral and CallBoundMethodGeneral now call vectorcall_function
  directly instead of going through FuncArgs + prepend_arg + invoke
- CallKwPy and CallKwBoundMethod use vectorcall_function with kwnames
- vectorcall_bound_method uses insert(0) on existing Vec instead of
  allocating a second Vec

* Auto-format: cargo fmt --all

* Fix vectorcall_native_function kwarg slice out-of-bounds

When needs_self was true and kwargs were present, pos_args only
contained positional args (self + original positionals) but
from_vectorcall expected kwarg values to follow in the slice.

Build the full args array (self + all original args including kwarg
values) before passing to from_vectorcall.

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