chore: rename quicproquo → quicprochat in Rust workspace

Rename all crate directories, package names, binary names, proto
package/module paths, ALPN strings, env var prefixes, config filenames,
mDNS service names, and plugin ABI symbols from quicproquo/qpq to
quicprochat/qpc.

crates/quicprochat-client/src/client/hex.rs

@@ -0,0 +1,7 @@
+pub fn encode(bytes: impl AsRef<[u8]>) -> String {
+    hex::encode(bytes)
+}
+
+pub fn decode(s: &str) -> Result<Vec<u8>, &'static str> {
+    hex::decode(s).map_err(|_| "invalid hex string")
+}