Rename ruff_python crate to ruff_python_stdlib (#3354)

In hindsight, `ruff_python` is too general. A good giveaway is that it's actually a prefix of some other crates. The intent of this crate is to reimplement pieces of the Python standard library and CPython itself, so `ruff_python_stdlib` feels appropriate.

crates/ruff_python_stdlib/src/lib.rs

@@ -0,0 +1,8 @@
+pub mod builtins;
+pub mod bytes;
+pub mod future;
+pub mod identifiers;
+pub mod keyword;
+pub mod str;
+pub mod sys;
+pub mod typing;