SDK Performance Boost

[lisandroct]

Description of Changes

It cleans up a couple of things to achieve better performance in the C# SDK:

1. It replaces the usage of LINQ (with direct for loops, for example);
2. Reduces the total amount of allocations by pooling arrays and avoiding some calls to .ToArray();
3. Reduces the initial size of websockets and resizes when necessary (this also reduces a lot of allocations).

API and ABI breaking changes

No changes. It's all internal.

Expected complexity level and risk

3. We need to make sure BSATN decoding stays consistent for all paths (I added a unit test for this) and that websockets behavior stays the same as before (just less memory hungry).

Testing

• Run benchmarks
• Tests all still pass

Benchmarks

I added two benchmarks:

xUnit Benchmarks:

Benchmark	Rows / Variant	Master mean	PR mean	Time delta	Master alloc	PR alloc	Alloc delta
DecompressDecodeMessage transaction_update	1, uncompressed	0.49 us	0.41 us	-16.3%	1,544 B	1,200 B	-344 B
DecompressDecodeMessage transaction_update	100, uncompressed	2.87 us	2.74 us	-4.5%	2,128 B	1,592 B	-536 B
DecompressDecodeMessage transaction_update	10,000, uncompressed	89.01 us	85.28 us	-4.2%	81,328 B	41,192 B	-40,136 B
DecompressDecodeMessage transaction_update	1, brotli	2.22 us	1.46 us	-34.2%	67,232 B	1,672 B	-65,560 B
DecompressDecodeMessage transaction_update	100, brotli	5.36 us	4.61 us	-14.0%	67,816 B	2,256 B	-65,560 B
DecompressDecodeMessage transaction_update	10,000, brotli	197.16 us	195.17 us	-1.0%	147,017 B	81,457 B	-65,560 B
Reducer/procedure payload	1	0.23 us	0.25 us	+8.7%	936 B	904 B	-32 B
Reducer/procedure payload	100	4.55 us	4.61 us	+1.3%	5,840 B	5,408 B	-432 B
Reducer/procedure payload	10,000	233.89 us	300.59 us	+28.5%	571,663 B	531,630 B	-40,033 B
DecompressDecodeMessage initial_connection	uncompressed	0.13 us	0.09 us	-30.8%	728 B	384 B	-344 B
DecompressDecodeMessage initial_connection	brotli	1.46 us	0.45 us	-69.2%	66,416 B	856 B	-65,560 B
Brotli inflate transaction_update	1	1.13 us	1.13 us	0.0%	936 B	936 B	0 B
Brotli inflate transaction_update	100	1.98 us	1.96 us	-1.0%	1,128 B	1,128 B	0 B
Brotli inflate transaction_update	10,000	109.13 us	108.40 us	-0.7%	40,728 B	40,710 B	-18 B
MultiDictionary.Apply	1	0.15 us	0.15 us	0.0%	872 B	872 B	0 B
MultiDictionary.Apply	100	8.42 us	8.41 us	-0.1%	43,544 B	43,544 B	0 B
MultiDictionary.Apply	10,000	1,202.86 us	1,174.74 us	-2.3%	4,234,208 B	4,234,253 B	+45 B
ParseRowList	1	0.05 us	0.05 us	0.0%	224 B	224 B	0 B
ParseRowList	100	3.22 us	3.28 us	+1.9%	2,600 B	2,600 B	0 B
ParseRowList	10,000	244.97 us	276.34 us	+12.8%	240,200 B	240,200 B	0 B

BenchmarkDotNet:
I started with the xUnit benchmark from above and I liked the look of the allocation deltas a lot. But the reducer/procedure time delta didn't look so nice, so I also added this BenchmarkDotNet project that should be a little more accurate and the equivalent benchmark (the first three) now look a lot more flat.

Benchmark	Rows	Master mean	PR mean	Time delta	Master alloc	PR alloc	Alloc delta
XUnitReducerProcedureShape	1	103.57 ns	112.14 ns	+8.3%	936 B	904 B	-32 B
XUnitReducerProcedureShape	100	1.394 us	1.422 us	+2.0%	5,840 B	5,408 B	-432 B
XUnitReducerProcedureShape	10,000	130.733 us	131.045 us	+0.2%	571,663 B	531,631 B	-40,032 B
SerializeAndDecodeFromByteArray	1	85.93 ns	82.72 ns	-3.7%	840 B	840 B	0 B
SerializeAndDecodeFromByteArray	100	1.359 us	1.376 us	+1.3%	4,944 B	4,944 B	0 B
SerializeAndDecodeFromByteArray	10,000	124.907 us	133.552 us	+6.9%	491,566 B	491,566 B	0 B
SerializeToListOnly	1	56.57 ns	57.33 ns	+1.3%	536 B	536 B	0 B
SerializeToListOnly	100	830.12 ns	845.00 ns	+1.8%	1,872 B	1,872 B	0 B
SerializeToListOnly	10,000	75.081 us	77.035 us	+2.6%	211,288 B	211,288 B	0 B
DecodeFromListOnly	1	45.78 ns	53.04 ns	+15.9%	400 B	368 B	-32 B
DecodeFromListOnly	100	582.62 ns	584.81 ns	+0.4%	3,968 B	3,536 B	-432 B
DecodeFromListOnly	10,000	56.498 us	52.541 us	-7.0%	360,373 B	320,340 B	-40,033 B
DecodeFromByteArrayOnly	1	41.55 ns	41.80 ns	+0.6%	368 B	368 B	0 B
DecodeFromByteArrayOnly	100	565.05 ns	566.06 ns	+0.2%	3,536 B	3,536 B	0 B
DecodeFromByteArrayOnly	10,000	50.594 us	55.436 us	+9.6%	320,340 B	320,340 B	0 B