perf: remove unnecessary allocation when writing http dates (#3261)

actix-http/benches/date-formatting.rs

@@ -0,0 +1,20 @@
+use std::time::SystemTime;
+
+use actix_http::header::HttpDate;
+use divan::{black_box, AllocProfiler, Bencher};
+
+#[global_allocator]
+static ALLOC: AllocProfiler = AllocProfiler::system();
+
+#[divan::bench]
+fn date_formatting(b: Bencher<'_, '_>) {
+    let now = SystemTime::now();
+
+    b.bench(|| {
+        black_box(HttpDate::from(black_box(now)).to_string());
+    })
+}
+
+fn main() {
+    divan::main();
+}