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/iteration6_resume_history.rs

@@ -166,7 +166,8 @@ fn hydration_reads_both_ok_and_err_records() {
     let project = Project::create_temp(tmp.path()).unwrap();
     let p = Persistence::new(project.path().to_path_buf());
     p.append_history("create table A with pk", false).unwrap();
-    p.append_history_failure("insert into A (1, 2, 3)", false).unwrap();
+    p.append_history_failure("insert into A (1, 2, 3)", false)
+        .unwrap();
     p.append_history("show data A", false).unwrap();
     let entries = p.read_recent_history(10).unwrap();
     assert_eq!(