feat: Add stbbr_for_presence_to for MUC join presence matching

- Add prime_for_presence_to() and prime_get_for_presence_to() in prime.c
- Add presence_to_callback() in server.c to handle MUC join presence
- Export stbbr_for_presence_to() in stabber.h
- Add stanzas_debug_last() for debugging failed verifications

src/server/prime.h

@@ -37,4 +37,7 @@ char* prime_get_for_id(const char *id);
 int prime_for_query(const char *query, char *stream);
 XMPPStanza* prime_get_for_query(const char *query);
 
+int prime_for_presence_to(const char *to_jid, char *stream);
+XMPPStanza* prime_get_for_presence_to(const char *to_jid);
+
 #endif