fix: resolve 7 code review issues from v0.4.x

- Fix KSUDP clutch field reading fuel at offset 59 (KSUDP has no clutch input)
- Replace Notify with watch::channel for reliable shutdown (no missed wakeups)
- Deduplicate read_u16 from parser_pcars into shared binary_utils
- Remove dead Display impl for FeedSource
- Remove unused read_i8 helper from binary_utils
- Change Vec<Instant> to [Instant; 50] in FeedState (eliminate heap alloc)
- Cache rarely-changing strings by driver_id in Telemetry Tool parser

src/parser_pcars.rs

@@ -366,15 +366,6 @@ fn parse_v2_car_physics(data: &[u8]) -> Result<TelemetryFrame, PcarsParseError>
     Ok(frame)
 }
 
-/// Read a u16 at the given offset (little-endian).
-fn read_u16(data: &[u8], offset: usize) -> u16 {
-    let buf: [u8; 2] = data
-        .get(offset..offset + 2)
-        .and_then(|s| s.try_into().ok())
-        .unwrap_or([0u8; 2]);
-    u16::from_le_bytes(buf)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;