NFTDescriptor snapshots fix #117

Job	Run time
IntegrationAsserts (AssertSwapEchidnaTest)	1m 14s
IntegrationInvariants (PropBalancesEchidnaTest)	1m 17s
IntegrationInvariants (PropReservesEchidnaTest)	1m 8s
UnitAsserts (BitMathEchidnaTest)	58s
UnitAsserts (FullMathEchidnaTest)	1m 11s
UnitAsserts (LiquidityMathEchidnaTest)	1m 4s
UnitAsserts (LowGasSafeMathEchidnaTest)	1m 5s
UnitAsserts (PriceMovementMathEchidnaTest)	1m 9s
UnitAsserts (TickMathEchidnaTest)	1m 7s
UnitAsserts (TickOverflowSafetyEchidnaTest)	1m 8s
UnitAsserts (TickTreeSearchEchidnaTest)	1m 11s
UnitAsserts (TickTreeEchidnaTest)	1m 7s
UnitAsserts (TokenDeltaMathEchidnaTest)	1m 19s
UnitAsserts (UnsafeMathEchidnaTest)	1m 7s
	16m 5s

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