Fix: Subspace broadcast filters non-radio devices (#22539)

* Please describe the intent of your changes in a clear fashion.
Addresses an `undefined variable` error (`canhear_range`) occurring in
`/proc/get_hearers_in_radio_ranges` when an
`/obj/item/implant/explosive` was present in the list of devices.

The root cause was identified in the `TRANSMISSION_SUBSPACE` path of
`/datum/signal/subspace/vocal/broadcast()`. Previously, this path would
copy all devices registered under `RADIO_CHAT` (which included the
explosive implant) into the `radios` list. Although a subsequent loop
attempted to filter out non-receivable devices, it would skip processing
non-`/obj/item/radio` types but not remove them from the list. This
meant the explosive implant, lacking a `canhear_range` variable, was
still passed to `get_hearers_in_radio_ranges`, causing the crash when
`radio.canhear_range` was accessed.

The fix modifies the `TRANSMISSION_SUBSPACE` logic to explicitly build
the `radios` list by iterating through `SSradio.get_devices` and only
adding actual `/obj/item/radio` instances that are capable of receiving
the signal. This ensures that `get_hearers_in_radio_ranges` only
receives valid radio objects, preventing the `canhear_range` error and
preserving the `as anything` keyword in the helper proc as it will now
always receive a correctly typed list.
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### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/example.dmi | ExamplePerson (Example Station) | CC0 |

Fixes SERVER-PROD-SR

---------

Co-authored-by: sentry[bot] <39604003+sentry[bot]@users.noreply.github.com>
Co-authored-by: VMSolidus <evilexecutive@gmail.com>

code/game/objects/structures/machinery/telecomms/broadcasting.dm

@@ -151,11 +151,9 @@
 		if (TRANSMISSION_SUBSPACE)
 			// Reach any radios on the levels
 			var/list/all_radios_of_our_frequency = SSradio.get_devices(frequency, RADIO_CHAT)
-			radios = all_radios_of_our_frequency.Copy()
-
-			for (var/obj/item/radio/subspace_radio in radios)
-				if(!subspace_radio.can_receive(frequency, signal_reaches_every_z_level))
-					radios -= subspace_radio
+			for (var/obj/item/radio/subspace_radio in all_radios_of_our_frequency)
+				if(subspace_radio.can_receive(frequency, signal_reaches_every_z_level))
+					radios += subspace_radio
 
 			// Cool antag radios can hear all Horizon comms
 			for (var/antag_freq in list(SYND_FREQ, RAID_FREQ, NINJ_FREQ))