Make the statement vector private on SemanticModel (#6348)

## Summary

Instead, expose these as methods, now that we can use a reasonable
nomenclature on the API.

crates/ruff_python_semantic/src/binding.rs

@@ -185,7 +185,7 @@ impl<'a> Binding<'a> {
     /// Returns the range of the binding's parent.
     pub fn parent_range(&self, semantic: &SemanticModel) -> Option<TextRange> {
         self.source
-            .map(|node_id| semantic.statements[node_id])
+            .map(|statement_id| semantic.statement(statement_id))
             .and_then(|parent| {
                 if parent.is_import_from_stmt() {
                     Some(parent.range())

crates/ruff_python_semantic/src/model.rs

@@ -31,7 +31,7 @@ pub struct SemanticModel<'a> {
     module_path: Option<&'a [String]>,
 
     /// Stack of all visited statements.
-    pub statements: Nodes<'a, Stmt>,
+    statements: Nodes<'a, Stmt>,
 
     /// The identifier of the current statement.
     statement_id: Option<NodeId>,
@@ -919,6 +919,29 @@ impl<'a> SemanticModel<'a> {
         None
     }
 
+    /// Return the [`Nodes`] vector of all statements.
+    pub const fn statements(&self) -> &Nodes<'a, Stmt> {
+        &self.statements
+    }
+
+    /// Return the [`NodeId`] corresponding to the given [`Stmt`].
+    #[inline]
+    pub fn statement_id(&self, statement: &Stmt) -> Option<NodeId> {
+        self.statements.node_id(statement)
+    }
+
+    /// Return the [`Stmt]` corresponding to the given [`NodeId`].
+    #[inline]
+    pub fn statement(&self, statement_id: NodeId) -> &'a Stmt {
+        self.statements[statement_id]
+    }
+
+    /// Given a [`Stmt`], return its parent, if any.
+    #[inline]
+    pub fn parent_statement(&self, statement: &'a Stmt) -> Option<&'a Stmt> {
+        self.statements.parent(statement)
+    }
+
     /// Set the [`Globals`] for the current [`Scope`].
     pub fn set_globals(&mut self, globals: Globals<'a>) {
         // If any global bindings don't already exist in the global scope, add them.