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/parser.rs

@@ -123,10 +123,8 @@ pub fn parse_head(buf: &[u8], max_headers: usize) -> Result<ParsedHead, ParseErr
             "connection" => {
                 connection_hdr = Some(value.to_ascii_lowercase());
             }
-            "expect" => {
-                if value.eq_ignore_ascii_case("100-continue") {
-                    expect_100 = true;
-                }
+            "expect" if value.eq_ignore_ascii_case("100-continue") => {
+                expect_100 = true;
             }
             _ => {}
         }