GeezerVison

Summary

Expose CPython 3.15 signatures for two cross-interpreter functions:

• _interpreters.new_config(name='isolated', /, **overrides)
• _interpreters.list_all(*, require_ready=False)

The wrappers move the original FuncArgs unchanged into the existing manual parsers. Their arity remains unbounded at the outer binder, the duplicate-keyword check cannot match any positional-or-keyword parameter, and callable flags remain as before. Defaults here are static signature metadata, not newly boxed runtime defaults. This PR does not claim complete argument/error parity for the underlying manual parsers. CPython's new_config calling-convention flag differs from RustPython's pre-existing flag.

The other _interpreters mismatches need separate work to preserve manual parser error precedence; this change does not depend on #9563.

Validation

• Independently source-reviewed against CPython v3.15.0 Modules/_interpretersmodule.c, generated Clinic signatures, RustPython's duplicate binding logic, and the current Report a missing argument before converting any #9513 precheck design.
• CPython 3.15.0 inspect.signature confirms both signatures; passing a positional name plus a keyword name still leaves the latter in overrides.
• prek hooks and git diff --check passed.
• No RustPython compilation or runtime execution was run locally; CI is needed.