feat(lib): Setting http1_writev(true) will now force writev queue usage

Previously, calling `http1_writev(true)` would just keep the default behavior, which was to auto detect if writev was optimal. Now, the auto-detection is still default, but explicitly calling `http1_writev(true)` will skip the auto-detection, and always use writev queue strategy.

Closes #2282

src/proto/h1/io.rs

@@ -94,6 +94,13 @@ where
         self.write_buf.set_strategy(WriteStrategy::Flatten);
     }
 
+    pub fn set_write_strategy_queue(&mut self) {
+        // this should always be called only at construction time,
+        // so this assert is here to catch myself
+        debug_assert!(self.write_buf.queue.bufs_cnt() == 0);
+        self.write_buf.set_strategy(WriteStrategy::Queue);
+    }
+
     pub fn read_buf(&self) -> &[u8] {
         self.read_buf.as_ref()
     }