fix(distributed): a server with no parent figures leaves our cap alone

The speed-derived child limit read a missing ratio as a refusal, so on any
server that never announces ParentSpeedRatio — soulfind among them — the
client carried no children at all, however it was configured. A ratio we
were never told is not a decision: the server's figures set the limit only
when it has given them, and otherwise the configured cap stands, which is
how slskd runs throughout. A speed below the announced minimum still means
none, which is the safety property the rule exists for.

Also stops repeating AcceptChildren: it is a standing state on the server,
so it goes out when the answer changes rather than on every message that
happens to prompt a recount.

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

@@ -1253,8 +1253,16 @@ impl Client {
     /// (`AcceptChildren`, code 100). Sent whenever that answer changes: the
     /// server only offers us to peers while it is true.
     fn announce_child_capacity(client_context: &Arc<RwLock<ClientContext>>) {
-        let (sender, has_room) = match client_context.read_safe() {
-            Ok(ctx) => (ctx.server_sender.clone(), ctx.children.has_room()),
+        let (sender, has_room) = match client_context.write_safe() {
+            Ok(mut ctx) => {
+                // Only on a change: the server holds this as a standing
+                // state, and repeating it on every message we happen to
+                // receive would be noise.
+                let Some(has_room) = ctx.accept_children_change() else {
+                    return;
+                };
+                (ctx.server_sender.clone(), has_room)
+            }
             Err(_) => return,
         };
         let Some(sender) = sender else { return };