fix: review findings on the protocol work

Correctness:
- A child that stopped reading could freeze the whole client: the relay
  writes under the context lock and the socket was blocking, so one stalled
  peer took every download, upload and API call with it. Child writes now
  have a deadline, and a child that hits it loses its slot.
- Relaying searches to children was gated by the leaf's answer budget, so a
  parent forwarded a fraction of the stream while advertising itself as
  healthy. The budget bounds our own share scan, which is what it was for;
  the tree's stream goes down whole.
- A dropped client kept its listener port for the life of the process, so a
  retried login advertised an ephemeral port nobody was told about. The
  listener is now stopped and the operations thread let go.
- Excluded phrases were compared against a lowercased path without being
  lowercased themselves, so a capitalised phrase never matched. They are
  normalised where they arrive.
- Losing our own operatorship wiped the room's whole operator roster,
  though we are still a member who can see it.
- A brokered ConnectToPeer of type D was logged and dropped; the peer is
  now told, since we never dial out to adopt a child.
- A peer request made with no server connection returned Ok and parked
  forever; it says NotConnected, as its docs always claimed.
- An empty interest was refused locally but still sent, leaving the
  server's list and ours permanently apart.

Simplification:
- Deleted the excluded-phrase helper nothing called, and the field doc that
  promised behaviour it never had.
- The four roster handlers and four standing handlers were eight
  constructors carrying constants their own message code already implies:
  one newtype each, 100 lines less.
- One place registers a search; the phrase list is borrowed, not cloned per
  relayed search.

soulseek-rs-lib/src/client/social.rs

@@ -301,7 +301,11 @@ impl Client {
     /// # Errors
     /// [`crate::SoulseekRs::NotConnected`] when there is no server connection.
     pub fn add_interest(&self, item: &str) -> Result<()> {
-        let item = self.context.write_safe()?.add_own_interest(item, true);
+        let Some(item) =
+            self.context.write_safe()?.add_own_interest(item, true)
+        else {
+            return Ok(()); // nothing to like or unlike
+        };
         self.send_server_message(MessageFactory::build_add_thing_i_like(&item))
     }
 
@@ -310,7 +314,11 @@ impl Client {
     /// # Errors
     /// [`crate::SoulseekRs::NotConnected`] when there is no server connection.
     pub fn remove_interest(&self, item: &str) -> Result<()> {
-        let item = self.context.write_safe()?.remove_own_interest(item, true);
+        let Some(item) =
+            self.context.write_safe()?.remove_own_interest(item, true)
+        else {
+            return Ok(()); // nothing to like or unlike
+        };
         self.send_server_message(MessageFactory::build_remove_thing_i_like(
             &item,
         ))
@@ -321,7 +329,11 @@ impl Client {
     /// # Errors
     /// [`crate::SoulseekRs::NotConnected`] when there is no server connection.
     pub fn add_dislike(&self, item: &str) -> Result<()> {
-        let item = self.context.write_safe()?.add_own_interest(item, false);
+        let Some(item) =
+            self.context.write_safe()?.add_own_interest(item, false)
+        else {
+            return Ok(()); // nothing to like or unlike
+        };
         self.send_server_message(MessageFactory::build_add_thing_i_hate(&item))
     }
 
@@ -330,7 +342,11 @@ impl Client {
     /// # Errors
     /// [`crate::SoulseekRs::NotConnected`] when there is no server connection.
     pub fn remove_dislike(&self, item: &str) -> Result<()> {
-        let item = self.context.write_safe()?.remove_own_interest(item, false);
+        let Some(item) =
+            self.context.write_safe()?.remove_own_interest(item, false)
+        else {
+            return Ok(()); // nothing to like or unlike
+        };
         self.send_server_message(MessageFactory::build_remove_thing_i_hate(
             &item,
         ))