Replaces `spawn()` in explosion code to `addtimer` and `INVOKE_ASYNC`. #2651

Job	Run time
Collect data for other tasks	8s
Run Linters	1m 35s
Alternate Tests	0s
Compile Maps	36s
Windows Build	48s
Check Alternate Tests	0s
Integration Tests (barrenquilla_mining) / run_integration_tests	7m 31s
Integration Tests (bigred_v2) / run_integration_tests	7m 38s
Integration Tests (deltastation) / run_integration_tests	8m 4s
Integration Tests (desparity) / run_integration_tests	7m 30s
Integration Tests (icy_caves) / run_integration_tests	7m 19s
Integration Tests (ice_colony_v2) / run_integration_tests	8m 57s
Integration Tests (gelida_iv) / run_integration_tests	8m 5s
Integration Tests (kutjevo) / run_integration_tests	6m 58s
Integration Tests (last_stand) / run_integration_tests	7m 0s
Integration Tests (lawanka) / run_integration_tests	8m 6s
Integration Tests (lv624) / run_integration_tests	7m 37s
Integration Tests (magmoor_digsite_iv) / run_integration_tests	8m 10s
Integration Tests (orion_outpost) / run_integration_tests	6m 51s
Integration Tests (oscar_outpost) / run_integration_tests	8m 1s
Integration Tests (prison_station_fop) / run_integration_tests	7m 18s
Integration Tests (research_outpost) / run_integration_tests	7m 20s
Integration Tests (slumbridge) / run_integration_tests	7m 40s
Integration Tests (talos) / run_integration_tests	7m 30s
Integration Tests (vapor_processing) / run_integration_tests	7m 4s
Integration Tests (whiskey_outpost_v2) / run_integration_tests	7m 6s
	2h 34m 52s

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