NTNet Extensibility (#22908)

Fixes https://github.com/Aurorastation/Aurora.3/issues/21944

Spiritual successor of
https://github.com/Aurorastation/Aurora.3/pull/22352
Cherrypicked changes from the C3 Crew Management branch, this PR
contains all NTNet extensibility features, including Field Relay
construction, off-site camera usage (contingent on standing up remote
hardware and being out of jamming), etc. This also fixes a handful of
outstanding telecomms and view/mobeye-related bugs adjacent to where I
was working.

changes:
- rscadd: "Adds NTNet extensibility, requires new machinery constructed
on away-site z-levels."
- rscadd: "Breaks NTNet Relay machinery into Quantum Relay ('core' obj
on Horizon) and Field Relay (deployable off-site constructions)."
- qol: "Embedded cameras (basically every video camera EXCEPT those
which are installed on walls) can now be viewed from NTNet-connected
z-level, not just connected ones."
- rscadd: "Adds several public camera monitor consoles to the Horizon
(near where public sensor grid feed consoles already exist)."
- rscadd: "Adds some spare camera console boards to Horizon technical
storage."
- qol: "Adds action button for 'cancel-camera-view' verb while viewing
cameras or looking up/down z-level."
- bugfix: "Fixes Jockey comms (frequency was missing from ANTAG_FREQS)."
- bugfix: "Fixes look-up/look-down actions intermittently failing
without first using cancel-camera-view."

code/modules/modular_computers/computers/modular_computer/core.dm

@@ -100,6 +100,8 @@
 /obj/item/modular_computer/Destroy()
 	STOP_PROCESSING(SSprocessing, src)
 
+	reset_remote_viewers(TRUE)
+
 	SStgui.close_uis(src)
 	enabled = FALSE
 
@@ -289,6 +291,7 @@
 		active_program = null
 	else
 		return FALSE
+	reset_remote_viewers()
 	var/mob/user = usr
 	if(user && istype(user) && !forced && !QDELETED(src))
 		INVOKE_ASYNC(src, TYPE_PROC_REF(/datum, ui_interact), user) // Re-open the UI on this computer. It should show the main screen now.
@@ -304,6 +307,14 @@
 		active_program = null
 	else
 		return FALSE
+	reset_remote_viewers()
+
+/obj/item/modular_computer/proc/reset_remote_viewers(var/unset_viewers_machine = FALSE)
+	for(var/mob/M in GLOB.player_list)
+		if(M.machine == src && M.is_viewing_remote_view())
+			if(unset_viewers_machine)
+				M.unset_machine()
+			M.reset_view(null)
 
 // Returns 0 for No Signal, 1 for Low Signal and 2 for Good Signal. 3 is for wired connection (always-on)
 /obj/item/modular_computer/proc/get_ntnet_status(var/specific_action = 0)