Added cancellableTaskValidation feature, tests, and documentation

[1eyewonder]

Proposed Changes

I added support for CancellableTaskValidation with relevant documentation and unit tests. I also fixed/updated some miscellaneous documentation

Types of changes

What types of changes does your code introduce to FsToolkit.ErrorHandling?
Put an x in the boxes that apply and remove ones that don't apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• Build and tests pass locally
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Further comments

As a 'quick-fix' I brought over some of the code which was in the FsToolkit.ErrorHandling.Tests project: Expect.fs, SampleDomain.fs, and TestData.fs for easier unit test implementation (copied and modified from AsyncValidation). I didn't know you wanted to create a shared test library for reduced code or if you wanted to keep things siloed from each other. I am open to either implementation

[TheAngryByrd]

❤️ This is so awesome.

As a 'quick-fix' I brought over some of the code which was in the FsToolkit.ErrorHandling.Tests project: Expect.fs, SampleDomain.fs, and TestData.fs for easier unit test implementation (copied and modified from AsyncValidation). I didn't know you wanted to create a shared test library for reduced code or if you wanted to keep things siloed from each other. I am open to either implementation

Yeah I've gone back and forth on this. Do whatever you feel is easier at this point. It's not much work to clean up later.

[1eyewonder]

I'm fine leaving it for now, and we can always decide later when looking at the job validation since that would technically need similar code

[TheAngryByrd]

Awesome start on this. Left some comments:

[TheAngryByrd]

This is a good start but I think we're also going to need tests for:

• Task
• Task<'T>
• Any awaitable (like Task.Yield()) (this should cover ValueTask/ValueTask<'T> as well)
• Async
• All these variants with Result/Validation as well.

Yeah this is gonna hurt.