Use ast::PythonVersion internally in the formatter and linter (#16170)

## Summary

This PR updates the formatter and linter to use the `PythonVersion`
struct from the `ruff_python_ast` crate internally. While this doesn't
remove the need for the `linter::PythonVersion` enum, it does remove the
`formatter::PythonVersion` enum and limits the use in the linter to
deserializing from CLI arguments and config files and moves most of the
remaining methods to the `ast::PythonVersion` struct.

## Test Plan

Existing tests, with some inputs and outputs updated to reflect the new
(de)serialization format. I think these are test-specific and shouldn't
affect any external (de)serialization.

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_wasm/src/lib.rs

@@ -1,6 +1,7 @@
 use std::path::Path;
 
 use js_sys::Error;
+use ruff_linter::settings::types::PythonVersion;
 use serde::{Deserialize, Serialize};
 use wasm_bindgen::prelude::*;
 
@@ -10,7 +11,6 @@ use ruff_linter::directives;
 use ruff_linter::line_width::{IndentWidth, LineLength};
 use ruff_linter::linter::check_path;
 use ruff_linter::registry::AsRule;
-use ruff_linter::settings::types::PythonVersion;
 use ruff_linter::settings::{flags, DEFAULT_SELECTORS, DUMMY_VARIABLE_RGX};
 use ruff_linter::source_kind::SourceKind;
 use ruff_linter::Locator;