Use HashSet instead of List for temporary check in transform handling

[peppy]

Noticed that this has no reason to be a list. Changing to HashSet avoids overheads from list capacity resizing.

[bdach]

While the choice of HashSet<T> makes sense here based on the ops executed on the collection, I do question the "list capacity resizing" claim a little bit. Hashsets aren't magic, they are also array-based and also resize. And the initial size of a hashset created via the parameterless ctor appears to be zero, which only then gets expanded to 3 on first add and then next prime larger than twice the previous one. This should generally match the exponential expand strategy a normal list uses and result in amortised constant insertion time. And a list starts with capacity 4.

So I'm not sure I'm seeing the overheads... Are there profiling results?

[peppy]

So I'm not sure I'm seeing the overheads... Are there profiling results?

Yeah, I'll provide at some point when I have the bandwidth. During gameplay there are some scenarios where transforms get cancelled a lot, and this becomes a top 5 allocator.

Can also cache to a private to improve things.

Also I read the hashset resize and it looked to be lower overhead than list, but maybe i misread.

[peppy]

Here's a comparison during 5 seconds of gameplay:

Before	After

I may switch this to use ArrayPool to avoid the retention overhead, not sure.

[peppy]

Also added benchmark coverage of this.

Method	Mean	Error	StdDev	Gen0	Allocated
CreateSingleBlank	4.048 ns	0.1419 ns	0.1457 ns	0.0230	96 B
CreateSequenceThenRewind	618,818.119 ns	4,703.7909 ns	3,927.8784 ns	7.8125	36689 B
CreateSequenceThenRewindManyChildren	867,089.049 ns	16,063.5529 ns	14,239.9213 ns	19.5313	83377 B
CreateSequenceThenClearAfter	4,342.572 ns	28.3819 ns	22.1587 ns	1.1139	4688 B
Expiry	29,001.144 ns	117.0617 ns	103.7722 ns	0.2747	1208 B
CreateSequenceWithDefaultEasing	1,192.490 ns	6.2673 ns	4.8931 ns	0.2861	1200 B
ApplySequenceWithDefaultEasing	367.749 ns	3.0380 ns	2.6931 ns	0.0648	272 B
CreateSequenceWithValueEasing	1,219.856 ns	9.6691 ns	8.0741 ns	0.2861	1200 B
ApplySequenceWithValueEasing	366.232 ns	1.4552 ns	1.1361 ns	0.0648	272 B
CreateSequenceWithReferenceEasing	1,286.804 ns	25.2288 ns	49.7993 ns	0.3033	1272 B
ApplySequenceWithReferenceEasing	382.487 ns	7.2113 ns	7.0824 ns	0.0706	296 B

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
CreateSingleBlank	4.126 ns	0.1401 ns	0.1376 ns	0.0229	-	96 B
CreateSequenceThenRewind	629,838.030 ns	8,592.5113 ns	7,617.0375 ns	0.9766	-	4689 B
CreateSequenceThenRewindManyChildren	872,620.208 ns	12,992.7174 ns	12,153.3959 ns	11.7188	0.9766	51342 B
CreateSequenceThenClearAfter	4,291.789 ns	20.7813 ns	18.4220 ns	1.1139	-	4688 B
Expiry	29,159.790 ns	271.9896 ns	227.1237 ns	0.2747	-	1208 B
CreateSequenceWithDefaultEasing	1,186.912 ns	14.5979 ns	12.1899 ns	0.2861	-	1200 B
ApplySequenceWithDefaultEasing	374.882 ns	6.6652 ns	6.5462 ns	0.0648	-	272 B
CreateSequenceWithValueEasing	1,234.310 ns	8.8299 ns	7.3734 ns	0.2861	-	1200 B
ApplySequenceWithValueEasing	375.117 ns	2.4284 ns	1.8959 ns	0.0648	-	272 B
CreateSequenceWithReferenceEasing	1,230.045 ns	11.3266 ns	9.4582 ns	0.3033	-	1272 B