Add stormtest concurrency/reload stress harness + docs #1110

Job	Run time
Godot tests / Linux	1m 14s
Game capture smoke / macOS	1m 23s
Game capture smoke / Linux	1m 21s
Stale server smoke / macOS	48s
Release smoke / ubuntu-latest	38s
Stale server smoke / Linux	42s
Godot tests / macOS	1m 28s
Godot tests / Linux (Godot 4.3)	1m 13s
Stale server smoke / Windows	1m 25s
Game capture smoke / Windows	3m 2s
Godot tests / Windows	3m 21s
Release smoke / windows-latest	1m 51s
Python 3.13 / ubuntu-latest	4m 11s
Python 3.11 / ubuntu-latest	2m 6s
Release smoke / macos-latest	50s
	25m 33s

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