Add support for System.IO.Pipelines

[smatsson]

This issue has been split from #116

Original PR: #123

Dev branch: pipelines-dev

[smatsson]

Initial testing looks good. Roughly half the memory usage :) Downside: A bit longer write times (marginal) and higher CPU usage. Still need to add unit tests and do some more benchmarking before releasing.

Might also add a build target for .NET6 as there are multiple huge performance improvements when it comes to file IO. Will wait for the final release of .NET6 before releasing that on nuget.

[smatsson]

Update: Stress test seems good. Currently investigating whether or not to enable pipelines by default.

[smatsson]

Stress test output. Test was 3 test runs with 50 simulations clients, each uploading 20 files (à 10 MB) without any file metadata. See source file: https://github.com/tusdotnet/tusdotnet/blob/pipelines-dev/Source/tusdotnet.performance/Program.cs#L30 (modified to not include metadata to only measure disk write performance). Test server was using a 11 GB RAM disk for writing files.

Pipelines

Test name	Avg memory used (MB)	Avg CPU usage (%)	Time taken (ms)
Pipelines 1	379	28	90 499
Pipelines 2	435	32	73 322
Pipelines 3	405	29	76 407

10 minutes after Pipelines 3: 0% CPU usage, 48 MB RAM

Streams

Test name	Avg memory used (MB)	Avg CPU usage (%)	Time taken (ms)
Streams 1	718	28	60 161
Streams 2	500	30	59 952
Streams 3	601	31	53 296

10 minutes after Streams 3: 0% CPU usage, 253 MB RAM