add build option debug-disk-pool to log disk buffers allocated by category #3201

Job	Run time
Simulations	2m 41s
Tests (crypto=built-in)	5m 14s
Tests (webtorrent=on deprecated-functions=off)	5m 50s
Build (crypto=built-in)	1m 35s
Build (release)	1m 4s
Build iOS	1m 45s
	18m 9s

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