StartAsTask -> StartImmediateAsTask

[TheAngryByrd]

Proposed Changes

Changes StartAsTask to StartImmediateAsTask for Async -> Task conversions. This should be a performance benefit as it's not starting on the threadpool everything.

See:

• Consider StartImmediateAsTask instead of StartAsTask to prevent a thread hop fsprojects/FSharp.Control.TaskSeq#135
• https://github.com/TheAngryByrd/IcedTasks/pull/17/files

Types of changes

What types of changes does your code introduce to FsToolkit.ErrorHandling?
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• Minor perf enhancement

Checklist

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• 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

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[abelbraaksma]

For reference, a similar fix has made it into F# Core as well: dotnet/fsharp#14499