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.

sdks/ruby/lib/quicprochat/errors.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module QuicProQuo
+  # Base error for quicproquo SDK.
+  class Error < StandardError; end
+
+  # OPAQUE authentication failed (bad credentials).
+  class AuthError < Error; end
+
+  # Operation timed out.
+  class TimeoutError < Error; end
+
+  # Client is not connected.
+  class NotConnectedError < Error; end
+
+  # Connection to the server failed.
+  class ConnectionError < Error; end
+end