Improve ruff_parse_simple to find UTF-8 violations (#5008)

Improves the `ruff_parse_simple` fuzz harness by adding checks for
parsed locations to ensure they all lie on UTF-8 character boundaries.
This will allow for faster identification of issues like #5004.

This also adds additional details for Apple M1 users and clarifies the
importance of using `init-fuzzer.sh` (thanks for the feedback,
@jasikpark 🙂).

crates/ruff_python_ast/src/prelude.rs

@@ -1,2 +1,3 @@
 pub use crate::node::AstNode;
 pub use rustpython_ast::*;
+pub use rustpython_parser::*;