Optimize Tasks collections in .Net 9

[LukaszRozmej]

Builds upon #7532

Changes

• Move task collections to pooled ones and use spans when using WaitAll, WhenAll and WhenAny

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

[rubo]

Nitpick: In some places we add items to the pool in a for loop with .Add(), in other places, with LINQ's .Select() or Enumerable.Range().Select(). Isn't it worth unifying the approach?