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.

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

crates/red_knot_python_semantic/src/program.rs

@@ -4,7 +4,7 @@ use crate::Db;
 
 use anyhow::Context;
 use ruff_db::system::{SystemPath, SystemPathBuf};
-use ruff_python_ast::python_version::PythonVersion;
+use ruff_python_ast::PythonVersion;
 use salsa::Durability;
 use salsa::Setter;