[style](trx-rs): fix clippy warnings for -D warnings CI

The CI lint job runs clippy with -D warnings, which surfaced a set of
existing warnings across decoders, the client, and the soapysdr backend.
Resolve them so the workspace is clean under the enforced lint level:

- collapsible_match / identity_op / needless_range_loop / same_item_push
  in trx-rds, trx-wspr, trx-vdes, trx-wefax, trx-aprs (mostly tests)
- field_reassign_with_default -> struct-update syntax in trx-client config
  tests
- assign_op_pattern, useless vec!, and test-module ordering picked up by
  cargo clippy --fix in trx-client and the soapysdr WFM tests

No behaviour changes; all affected crates' tests pass.

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-wspr/src/protocol.rs

@@ -483,7 +483,7 @@ mod tests {
         let c4 = idx27(b'T');
         let c5 = idx27(b' ');
         let n1 = ((c0 * 36 + c1) * 10 + c2) * 27u32.pow(3) + c3 * 27u32.pow(2) + c4 * 27 + c5;
-        let m1 = (179 - 10 * 5 - 2) * 180 + 10 * 13 + 0; // FN20
+        let m1 = (179 - 10 * 5 - 2) * 180 + 10 * 13; // FN20 (final term is 0)
         let power_code = 37u32;
 
         let mut input_bits = [0u8; NBITS];
@@ -530,8 +530,8 @@ mod tests {
     fn interleave_deinterleave_roundtrip() {
         // Create a sequence of distinguishable values
         let mut original = [0u8; NSYMS];
-        for i in 0..NSYMS {
-            original[i] = (i % 256) as u8;
+        for (i, slot) in original.iter_mut().enumerate() {
+            *slot = (i % 256) as u8;
         }
 
         let interleaved = interleave(&original);