Emergency shuttle is aware of security level (#78271)

## About The Pull Request

The emergency shuttle maintains its security level coefficient and does
the calculation instead of outside procs that aren't aware of what alert
it was when the shuttle was first called.

If the shuttle auto-call timer should be capped at the current security
level timer, that can be done in a different PR.

## Why It's Good For The Game

Fixes https://github.com/tgstation/tgstation/issues/78159

## Changelog

🆑 LT3
fix: Emergency shuttle should correctly scale timer up/down when
changing security levels
/🆑

code/modules/security_levels/security_level_datums.dm

@@ -45,7 +45,7 @@
 	sound = 'sound/misc/notice2.ogg' // Friendly beep
 	number_level = SEC_LEVEL_GREEN
 	lowering_to_configuration_key = /datum/config_entry/string/alert_green
-	shuttle_call_time_mod = 2
+	shuttle_call_time_mod = ALERT_COEFF_GREEN
 
 /**
  * BLUE
@@ -58,7 +58,7 @@
 	number_level = SEC_LEVEL_BLUE
 	lowering_to_configuration_key = /datum/config_entry/string/alert_blue_downto
 	elevating_to_configuration_key = /datum/config_entry/string/alert_blue_upto
-	shuttle_call_time_mod = 1
+	shuttle_call_time_mod = ALERT_COEFF_BLUE
 
 /**
  * RED
@@ -71,7 +71,7 @@
 	number_level = SEC_LEVEL_RED
 	lowering_to_configuration_key = /datum/config_entry/string/alert_red_downto
 	elevating_to_configuration_key = /datum/config_entry/string/alert_red_upto
-	shuttle_call_time_mod = 0.5
+	shuttle_call_time_mod = ALERT_COEFF_RED
 
 /**
  * DELTA
@@ -83,4 +83,4 @@
 	sound = 'sound/misc/airraid.ogg' // Air alarm to signify importance
 	number_level = SEC_LEVEL_DELTA
 	elevating_to_configuration_key = /datum/config_entry/string/alert_delta
-	shuttle_call_time_mod = 0.25
+	shuttle_call_time_mod = ALERT_COEFF_DELTA