[style](trx-ais): drop redundant u32 cast

get_uint returns Option<u32>, so `? as u32` is an unnecessary same-type
cast flagged by clippy under -D warnings (rust 1.97).

Assisted-By: Claude Code (claude-opus-4)
Claude-Session: https://claude.ai/code/session_01NFpGtGTWUEYXLwZeZs2RAV
Signed-off-by: Stan Grams <sjg@haxx.space>

src/decoders/trx-ais/src/lib.rs

@@ -243,7 +243,7 @@ fn parse_frame(frame: RawFrame, channel: &str) -> Option<AisMessage> {
 
     let message_type = get_uint(&bits, 0, 6)? as u8;
     let repeat = get_uint(&bits, 6, 2)? as u8;
-    let mmsi = get_uint(&bits, 8, 30)? as u32;
+    let mmsi = get_uint(&bits, 8, 30)?;
 
     let mut msg = AisMessage {
         rig_id: None,