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.

src/seed/check.rs

@@ -18,7 +18,11 @@ pub fn parse_in_check_values(check: &str, column: &str) -> Option<Vec<String>> {
         return None;
     }
     let values = extract_quoted_list(&check[paren_open..])?;
-    if values.is_empty() { None } else { Some(values) }
+    if values.is_empty() {
+        None
+    } else {
+        Some(values)
+    }
 }
 
 const fn is_ident_byte(b: u8) -> bool {
@@ -45,8 +49,8 @@ fn find_in_paren(check: &str) -> Option<(usize, usize)> {
             i += 1;
             continue;
         }
-        let is_in = (b == b'i' || b == b'I')
-            && bytes.get(i + 1).is_some_and(|n| *n == b'n' || *n == b'N');
+        let is_in =
+            (b == b'i' || b == b'I') && bytes.get(i + 1).is_some_and(|n| *n == b'n' || *n == b'N');
         if is_in {
             let before_ok = i == 0 || !is_ident_byte(bytes[i - 1]);
             let after = i + 2;