`parse_arguments` reads a caller-supplied pointer as a slice

`parse_arguments` is safe. It takes `arguments: *const AnyObject` and `argc`, and calls `slice::from_raw_parts(arguments, argc as usize)`.

It does not check that `arguments` is non-null and aligned, or that `argc` elements are initialized. Safe Rust can pass a null pointer or a length past the allocation. The maintainer confirmed this on 2026-10-03, including a debug abort on Rust 1.78+ when Ruby calls an arity -1 method (`to_s` via `format`, `puts`, or `Array#join`) with a NULL `argv` and `argc` of 0.