fix(mam, log): improve datetime handling and memory management in MAM and log fetching

- Introduce static helper `_truncate_datetime_suffix()` to safely trim datetime strings, removing unwanted suffixes like timezone offsets
- Replace manual string management with auto_gchar and g_strdup for safer, clearer ownership and to prevent leaks
- Add safety checks and logging warnings for unexpected datetime string lengths or null pointers
- Refactor _mam_rsm_id_handler to use the helper function and updated string handling
- Change log_database_get_previous_chat parameters for consistent ownership semantics, avoiding double frees and mem leaks
- Overall improve stability and prevent memory leaks during log database queries

src/xmpp/presence.c

@@ -644,7 +644,7 @@ _available_handler(xmpp_stanza_t* const stanza)
         const char* account_name = session_get_account_name();
         int max_sessions = accounts_get_max_sessions(account_name);
         if (max_sessions > 0) {
-            const gchar* cur_resource = accounts_get_resource(account_name);
+            auto_gchar gchar* cur_resource = accounts_get_resource(account_name);
             int res_count = connection_count_available_resources();
             if (res_count > max_sessions && g_strcmp0(cur_resource, resource->name)) {
                 ProfWin* console = wins_get_console();