test: proptest suite for protocol and COBS framing

Ten properties covering: RadioConfig roundtrip and validate/resolve
determinism; no-panic on arbitrary bytes for both Command::from_bytes
and RadioConfig::from_bytes; bounded-capacity for Transmit payloads
(guards the heapless::Vec size); Command roundtrip via a test-only
encoder (the library only decodes commands); COBS reversibility; and
two streaming CobsDecoder properties (no-panic on random byte streams
with random chunk boundaries, and a full encode→feed→decode roundtrip).

Adds Clone to Command and Response — benign public-API expansion that
unblocks proptest's Just strategy.

src/lib.rs

@@ -156,7 +156,7 @@ impl RadioConfig {
 
 /// Host → firmware commands.
 #[allow(clippy::large_enum_variant)]
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Command {
     Ping,
     GetConfig,
@@ -220,7 +220,7 @@ impl Command {
 
 /// Firmware → host responses.
 #[allow(clippy::large_enum_variant)]
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Response {
     Pong,
     Config(RadioConfig),