dbus-manager: limit the number of states/patterns per query (#41891)

Let's cap the number of states/patterns per query to something
reasonable, i.e. max 256 states and 4K patterns per query.

---

Also, use the env assignments limit in a couple more places.

src/basic/env-util.h

@@ -3,6 +3,8 @@
 
 #include "basic-forward.h"
 
+#define ENVIRONMENT_ASSIGNMENTS_MAX 16384U
+
 size_t sc_arg_max(void);
 
 bool env_name_is_valid(const char *e);