New block evaluation `Budget` system replacing `depth`. #318

Job	Run time
no_std	27s
build (ubuntu, stable, locked, true)	11m 41s
miri	1m 33s
build (windows, stable, locked, false)	23m 2s
build (macos, stable, locked, false)	24m 12s
build (ubuntu, nightly, locked, false)	21m 23s
build (ubuntu, beta, locked, false)	22m 50s
build (ubuntu, stable, latest, false)	17m 31s
build (ubuntu, stable, minimal, false)	14m 55s
deploy	17s
fuzz	15m 17s
features	26m 5s
	2h 59m 13s

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