[red-knot] Unify setup_db() functions, add TestDb builder (#14777)

## Summary

- Instead of seven (more or less similar) `setup_db` functions, use just
one in a single central place.
- For every test that needs customization beyond that, offer a
`TestDbBuilder` that can control the Python target version, custom
typeshed, and pre-existing files.

The main motivation for this is that we're soon going to need
customization of the Python version, and I didn't feel like adding this
to each of the existing `setup_db` functions.

crates/red_knot_python_semantic/src/semantic_model.rs

@@ -166,31 +166,15 @@ impl_binding_has_ty!(ast::ParameterWithDefault);
 mod tests {
     use ruff_db::files::system_path_to_file;
     use ruff_db::parsed::parsed_module;
-    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
 
-    use crate::db::tests::TestDb;
-    use crate::program::{Program, SearchPathSettings};
-    use crate::python_version::PythonVersion;
-    use crate::{HasTy, ProgramSettings, SemanticModel};
-
-    fn setup_db<'a>(files: impl IntoIterator<Item = (&'a str, &'a str)>) -> anyhow::Result<TestDb> {
-        let mut db = TestDb::new();
-        db.write_files(files)?;
-
-        Program::from_settings(
-            &db,
-            &ProgramSettings {
-                target_version: PythonVersion::default(),
-                search_paths: SearchPathSettings::new(SystemPathBuf::from("/src")),
-            },
-        )?;
-
-        Ok(db)
-    }
+    use crate::db::tests::TestDbBuilder;
+    use crate::{HasTy, SemanticModel};
 
     #[test]
     fn function_ty() -> anyhow::Result<()> {
-        let db = setup_db([("/src/foo.py", "def test(): pass")])?;
+        let db = TestDbBuilder::new()
+            .with_file("/src/foo.py", "def test(): pass")
+            .build()?;
 
         let foo = system_path_to_file(&db, "/src/foo.py").unwrap();
 
@@ -207,7 +191,9 @@ mod tests {
 
     #[test]
     fn class_ty() -> anyhow::Result<()> {
-        let db = setup_db([("/src/foo.py", "class Test: pass")])?;
+        let db = TestDbBuilder::new()
+            .with_file("/src/foo.py", "class Test: pass")
+            .build()?;
 
         let foo = system_path_to_file(&db, "/src/foo.py").unwrap();
 
@@ -224,10 +210,10 @@ mod tests {
 
     #[test]
     fn alias_ty() -> anyhow::Result<()> {
-        let db = setup_db([
-            ("/src/foo.py", "class Test: pass"),
-            ("/src/bar.py", "from foo import Test"),
-        ])?;
+        let db = TestDbBuilder::new()
+            .with_file("/src/foo.py", "class Test: pass")
+            .with_file("/src/bar.py", "from foo import Test")
+            .build()?;
 
         let bar = system_path_to_file(&db, "/src/bar.py").unwrap();