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/typing_surface/create_m2n.rs

@@ -67,7 +67,10 @@ fn create_m2n_with_as_name_parses() {
 #[test]
 fn after_as_keyword_is_incomplete() {
     let schema = schema_multi_table();
-    let a = assess_at_end("create m:n relationship from Customers to Orders as ", &schema);
+    let a = assess_at_end(
+        "create m:n relationship from Customers to Orders as ",
+        &schema,
+    );
     assert!(matches!(a.state, InputState::IncompleteAtEof));
     crate::snap!("after_as", a);
 }