Ideas for reducing the time required to run all benchmarks

[adamsitnik]

@jorive I am going to add all the ideas I have here and one day we can start the improvements from here.

1. PingPong benchmark from System.Threading.Channels.Tests takes 2.5s to execute. It's executed for 3 channels, up to 20 times for each of them. 2.5 x 3 x 20 = 150 seconds. The solution would be to change the inner iteration count from 1_000_000 to 1_000 or any other smaller value. fixed in Remove inner iteration counts from the benchmarks #126

[adamsitnik]

Another idea: introduce "Priority" categories. Example: we have benchmarks for non-generic collections, which should not be used by the people who care about performance. We can run those tests only before a major release, not with every CI urn