Introduce SourceCodeSlice to reduce the size of FormatElement (#4622)

Introduce `SourceCodeSlice` to reduce the size of `FormatElement`

crates/ruff_python_formatter/src/context.rs

@@ -1,36 +1,34 @@
-use std::rc::Rc;
-
-use ruff_formatter::{FormatContext, SimpleFormatOptions};
+use ruff_formatter::{FormatContext, SimpleFormatOptions, SourceCode};
 use ruff_python_ast::source_code::Locator;
 
-pub struct ASTFormatContext {
+#[derive(Clone, Debug)]
+pub struct ASTFormatContext<'source> {
     options: SimpleFormatOptions,
-    contents: Rc<str>,
+    contents: &'source str,
 }
 
-impl ASTFormatContext {
-    pub fn new(options: SimpleFormatOptions, contents: &str) -> Self {
-        Self {
-            options,
-            contents: Rc::from(contents),
-        }
+impl<'source> ASTFormatContext<'source> {
+    pub fn new(options: SimpleFormatOptions, contents: &'source str) -> Self {
+        Self { options, contents }
+    }
+
+    pub fn contents(&self) -> &'source str {
+        self.contents
+    }
+
+    pub fn locator(&self) -> Locator<'source> {
+        Locator::new(self.contents)
     }
 }
 
-impl FormatContext for ASTFormatContext {
+impl FormatContext for ASTFormatContext<'_> {
     type Options = SimpleFormatOptions;
 
     fn options(&self) -> &Self::Options {
         &self.options
     }
-}
 
-impl ASTFormatContext {
-    pub fn contents(&self) -> Rc<str> {
-        self.contents.clone()
-    }
-
-    pub fn locator(&self) -> Locator {
-        Locator::new(&self.contents)
+    fn source_code(&self) -> SourceCode {
+        SourceCode::new(self.contents)
     }
 }