BotServ: BOTSTATS per-channel activity

BOTSTATS <#channel> reports the lines the bot has seen this session and
the top talkers. Tracked live in the network view (bounded per-nick map),
recorded for bot-assigned channels only, and also fed to the shared stats
registry as botserv.messages.

botserv/src/stats.rs

@@ -0,0 +1,25 @@
+use fedserv_api::{NetView, Sender, ServiceCtx, Store};
+
+// BOTSTATS <#channel>: session activity the bot has seen in a channel — total
+// lines and the top talkers. Founder-or-admin.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, net: &dyn NetView, db: &mut dyn Store) {
+    let Some(&chan) = args.get(1) else {
+        ctx.notice(me, from.uid, "Syntax: BOTSTATS <#channel>");
+        return;
+    };
+    if !super::require_channel_admin(me, from, chan, ctx, db) {
+        return;
+    }
+    let Some((lines, top)) = net.channel_activity(chan) else {
+        ctx.notice(me, from.uid, format!("No activity recorded for \x02{chan}\x02 yet."));
+        return;
+    };
+    ctx.notice(me, from.uid, format!("\x02{chan}\x02 — \x02{lines}\x02 line(s) seen this session."));
+    if top.is_empty() {
+        return;
+    }
+    ctx.notice(me, from.uid, "Top talkers:");
+    for (i, (nick, count)) in top.iter().enumerate() {
+        ctx.notice(me, from.uid, format!("  {}. \x02{nick}\x02 — {count}", i + 1));
+    }
+}