GetCallStateTool
Returns the device call state from android.telephony.TelephonyManager. The deprecated callState getter needs READ_PHONE_STATE: without it, apps targeting API < 31 silently get CALL_STATE_IDLE (so this tool may falsely report "idle"), while apps targeting API 31+ get a SecurityException instead — caught here and surfaced as a clear error rather than a generic failure. Output: state ("idle" | "ringing" | "active" | "unknown").