[fix](trx-rs): add EMA smoothing to signal strength and fix freq input clobbering

EMA (α=0.4) smooths the carrier power estimate across DSP blocks. Custom PartialEq on VchanRdsEntry excludes signal_db so rapidly-changing levels do not trigger main state SSE updates that overwrite the frequency input.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-core/src/rig/state.rs

@@ -430,7 +430,11 @@ pub struct RdsData {
 }
 
 /// RDS metadata snapshot for a virtual channel.
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+///
+/// `PartialEq` intentionally ignores `signal_db` so that rapidly-changing
+/// signal levels do not cause the main state snapshot to diff on every poll
+/// cycle (signal_db flows through the spectrum SSE instead).
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct VchanRdsEntry {
     /// Virtual channel UUID.
     pub id: Uuid,
@@ -442,6 +446,12 @@ pub struct VchanRdsEntry {
     pub signal_db: Option<f32>,
 }
 
+impl PartialEq for VchanRdsEntry {
+    fn eq(&self, other: &Self) -> bool {
+        self.id == other.id && self.rds == other.rds
+    }
+}
+
 /// Read-only projection of state shared with clients.
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
 pub struct RigSnapshot {