style: apply rustfmt across all crates and demos

Consistent formatting pass: line wrapping, import sorting, trailing
whitespace removal, let-chain indentation, merged derive attributes,
and unsafe block reformatting.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

demos/rtx-cardiosim-demo/src/ecg.rs

@@ -15,7 +15,7 @@ pub struct ECGComputer {
 
 impl ECGComputer {
     /// Create a new ECG computer.
-    #[must_use] 
+    #[must_use]
     pub fn new(leads: &ECGLeads) -> Self {
         let mut electrode_positions = leads.custom_electrodes.clone();