chore: prepare 0.1.0 for crates.io publish

- Cargo.toml: add documentation and readme fields; expand the exclude
  list so deny.toml, justfile, mise.toml, .github, .jj, fuzz, and any
  cargo-mutants output never ship in the published tarball.
- README: badges, install snippet for both feature shapes, testing
  matrix.
- CHANGELOG.md: keep-a-changelog skeleton with a 0.1.0 entry.
- Revert framing.rs let-chain back to nested if-let so the published
  MSRV holds at the edition-2024 floor (1.85). Behaviour unchanged.

cargo publish --dry-run packages cleanly.

src/framing.rs

@@ -55,9 +55,10 @@ impl CobsDecoder {
                 if self.len > 0 {
                     let mut decode_buf = [0u8; MAX_FRAME];
                     if let Some(decoded_len) = ucobs::decode(&self.buf[..self.len], &mut decode_buf)
-                        && let Some(cmd) = Command::from_bytes(&decode_buf[..decoded_len])
                     {
-                        on_command(cmd);
+                        if let Some(cmd) = Command::from_bytes(&decode_buf[..decoded_len]) {
+                            on_command(cmd);
+                        }
                     }
                 }
                 self.len = 0;