chore: fix all clippy warnings across workspace

assets/screenshot.txt

@@ -0,0 +1,59 @@
+=== Alice (left) ===
+❯ ./target/debug/qpq repl --username alice --password de
+opass1 --server 127.0.0.1:17123 --ca-cert /tmp/tmp.adbXG
+OrPY/server-cert.der --state /tmp/tmp.adbXGLOrPY/alice.b
+n
+  registering 'alice'...
+  user 'alice' registered
+  logging in as 'alice'...
+  logged in, session cached
+  identity: c1e1f6df17eeb6f539d7fbea94129fa32fc02ca40e5c
+7a7c95cfc94161d5f628
+  KeyPackage uploaded
+  hybrid key uploaded
+  type /help for commands, Ctrl+D to exit
+
+[no conversation] > /dm bob
+  resolving bob...
+  creating channel...
+  fetching peer's key package...
+  DM with @bob created. Start typing!
+[@bob] > ^LHey Bob, testing our E2E encrypted channel!
+[@bob] > Right. MLS forward secrecy + post-quantum KEM.
+[@bob] > /group-info
+  Conversation: @bob
+  Type: DM
+  Members: 2
+    alice (you), bob
+  MLS epoch: 1
+[@bob] >
+
+=== Bob (right) ===
+❯ ./target/debug/qpq repl --username bob --password demop
+ass2 --server 127.0.0.1:17123 --ca-cert /tmp/tmp.adbXGLOr
+PY/server-cert.der --state /tmp/tmp.adbXGLOrPY/bob.bin
+  registering 'bob'...
+  user 'bob' registered
+  logging in as 'bob'...
+  logged in, session cached
+  identity: a8c2f19f1b080616b7206e02244fd14c2ab8821367392
+af5ff9c89c69750c73f
+  KeyPackage uploaded
+  hybrid key uploaded
+  type /help for commands, Ctrl+D to exit
+
+[no conversation] > /list
+  no conversations yet. Try /dm <username> or /create-gro
+up <name>
+[no conversation] > /switch @alice
+  error: conversation not found: @alice
+[no conversation] > ^LWorks great -- the server never see
+s plaintext?
+  error: no active conversation; use /dm or /create-group
+ first
+[no conversation] > /whoami
+  identity: a8c2f19f1b080616b7206e02244fd14c2ab8821367392
+af5ff9c89c69750c73f
+  hybrid key: yes
+  conversations: 0
+[no conversation] >