chore(clippy): appease 1.97 lints — derive Default, collapse ifs, drop needless borrow

Pre-existing, surfaced by the toolchain bump (rust-version is 1.95; the
sandbox gates with stable 1.97). All four are cargo clippy --fix output
with the mechanical-collapse indentation hand-tidied to house style;
the parser change is semantics-preserving (a non-100-continue Expect
value now falls to the _ arm instead of an empty if — headers.append
still runs after the match either way). No fmt pass: rustfmt would
clobber the aligned-assignment style, so only the touched lines moved.

src/conn_actor.rs

@@ -157,10 +157,10 @@ pub fn run_connection(
         // If client sent `Expect: 100-continue`, emit it before reading the
         // body. RFC 7231 §5.1.1. We don't gate on app logic here; v1 always
         // accepts.
-        if parsed.expect_100 {
-            if write_all(raw, b"HTTP/1.1 100 Continue\r\n\r\n", Instant::now() + limits.write_timeout).is_err() {
-                return;
-            }
+        if parsed.expect_100
+            && write_all(raw, b"HTTP/1.1 100 Continue\r\n\r\n", Instant::now() + limits.write_timeout).is_err()
+        {
+            return;
         }
 
         // `consumed_past_head`: how many RAW bytes of `buf` past the head