Improve numerical stability of fwd gradients for std_normal_log_qf #4871

Job	Run time
mix fun and prob tests 3 (windows-11-arm)	42m 12s
mix fun and prob tests 4 (windows-11-arm)	37m 15s
mix fun and prob tests 2 (windows-11-arm)	40m 9s
mix fun and prob tests 1 (windows-11-arm)	46m 0s
mix fun and prob tests 5 (windows-latest)	1h 42m 33s
mix fun and prob tests 2 (windows-latest)	46m 37s
mix fun and prob tests 1 (windows-latest)	41m 11s
mix fun and prob tests 5 (windows-11-arm)	1h 30m 47s
mix fun and prob tests 1 (ubuntu-24.04-arm)	28m 9s
mix fun and prob tests 3 (windows-latest)	40m 35s
mix fun and prob tests 2 (ubuntu-24.04-arm)	33m 43s
mix fun and prob tests 4 (windows-latest)	30m 57s
rev tests (windows-11-arm)	26m 47s
misc tests (windows-11-arm)	8m 55s
fwd tests (windows-11-arm)	10m 2s
mix fun and prob tests 3 (ubuntu-24.04-arm)	29m 54s
mix fun and prob tests 4 (ubuntu-24.04-arm)	22m 53s
mix fun and prob tests 5 (ubuntu-24.04-arm)	1h 7m 6s
non-fun mix tests (windows-11-arm)	12m 49s
fwd tests (windows-latest)	9m 51s
prim tests (windows-latest)	1h 33m 33s
rev tests (windows-latest)	41m 10s
misc tests (ubuntu-24.04-arm)	4m 6s
fwd tests (ubuntu-24.04-arm)	4m 36s
rev tests (ubuntu-24.04-arm)	19m 23s
prim tests (ubuntu-24.04-arm)	43m 19s
non-fun mix tests (ubuntu-24.04-arm)	6m 7s
prim tests (windows-11-arm)	55m 12s
misc tests (windows-latest)	5m 32s
non-fun mix tests (windows-latest)	11m 31s
	17h 32m 54s

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