style: format the whole tree with cargo fmt (stock defaults, #35)

One-time, mechanical reformat — no functional changes. The tree was not
rustfmt-clean (~1800 hunks across ~100 files); this brings it to stock
`cargo fmt` defaults so a `cargo fmt --check` CI gate can follow.
Behaviour-preserving: 2509 pass / 0 fail / 1 ignored (unchanged baseline),
clippy clean. A .git-blame-ignore-revs entry follows so `git blame`
skips this commit.

tests/it/iteration2_persistence.rs

@@ -14,9 +14,7 @@ use std::path::Path;
 use rdbms_playground::db::Database;
 use rdbms_playground::dsl::{ColumnSpec, ReferentialAction, RowFilter, Type, Value};
 use rdbms_playground::persistence::Persistence;
-use rdbms_playground::project::{
-    self, DATA_DIR, PROJECT_YAML,
-};
+use rdbms_playground::project::{self, DATA_DIR, PROJECT_YAML};
 
 fn tempdir() -> tempfile::TempDir {
     tempfile::tempdir().expect("create tempdir")
@@ -33,9 +31,7 @@ fn rt() -> tokio::runtime::Runtime {
 /// `Database` (with persistence wired) plus the path so the
 /// test can inspect on-disk state. The project is held alive
 /// implicitly via the leaked `TempDir` returned alongside.
-fn open_project(
-    data: &tempfile::TempDir,
-) -> (project::Project, Database, std::path::PathBuf) {
+fn open_project(data: &tempfile::TempDir) -> (project::Project, Database, std::path::PathBuf) {
     let project = project::open_or_create(None, Some(data.path())).expect("open project");
     let path = project.path().to_path_buf();
     let persistence = Persistence::new(path.clone());
@@ -72,7 +68,10 @@ fn create_table_writes_yaml_and_history() {
     });
 
     let yaml = read_yaml(&path);
-    assert!(yaml.contains("- name: Customers"), "yaml missing table:\n{yaml}");
+    assert!(
+        yaml.contains("- name: Customers"),
+        "yaml missing table:\n{yaml}"
+    );
     assert!(yaml.contains("primary_key: [id]"), "yaml: {yaml}");
     assert!(yaml.contains("type: serial"), "yaml: {yaml}");
     assert!(yaml.contains("type: text"), "yaml: {yaml}");
@@ -151,9 +150,15 @@ fn drop_table_removes_its_csv() {
         .unwrap();
     });
 
-    assert!(read_csv(&path, "Customers").is_none(), "CSV should be deleted");
+    assert!(
+        read_csv(&path, "Customers").is_none(),
+        "CSV should be deleted"
+    );
     let yaml = read_yaml(&path);
-    assert!(!yaml.contains("- name: Customers"), "table should be gone from yaml:\n{yaml}");
+    assert!(
+        !yaml.contains("- name: Customers"),
+        "table should be gone from yaml:\n{yaml}"
+    );
 }
 
 #[test]
@@ -263,7 +268,10 @@ fn create_table_does_not_write_csv_for_empty_table() {
 
     // Schema landed in YAML.
     let yaml = read_yaml(&path);
-    assert!(yaml.contains("- name: Customers"), "yaml missing table:\n{yaml}");
+    assert!(
+        yaml.contains("- name: Customers"),
+        "yaml missing table:\n{yaml}"
+    );
     // ...but no CSV until there's data.
     assert!(
         read_csv(&path, "Customers").is_none(),
@@ -394,7 +402,10 @@ fn project_yaml_carries_relationship_after_add() {
     });
 
     let yaml = read_yaml(&path);
-    assert!(yaml.contains("- name: Customers_id_to_Orders_CustId"), "yaml: {yaml}");
+    assert!(
+        yaml.contains("- name: Customers_id_to_Orders_CustId"),
+        "yaml: {yaml}"
+    );
     assert!(yaml.contains("on_delete: cascade"), "yaml: {yaml}");
     assert!(yaml.contains("on_update: no_action"), "yaml: {yaml}");
 }