Adds cancellation token support for long running work grains.

[Kritner]

Description

This is a breaking change to the package, as now implementations of grains need to have the additional parameter of GrainCancellationToken added.

Previous signature that needed implementing:

protected abstract Task<TResult> PerformWork(TRequest request);

New signature:

protected abstract Task<TResult> PerformWork(
  TRequest request, GrainCancellationToken grainCancellationToken);

You will be safe to just add this parameter to all of your long running grain implementations, but now you have the option of performing cancellation logic (added a few tests to demonstrate this)

• CancellationTokens now provided to sync work grain execution through a Start overload.
• Old Start method is still available, and just news up a cancellation token for backwards compatibility.
• Grain implementations can decide what to do (or not) when a cancellation signal is received.
  • This could be to return an intermediate (but perhaps incomplete?) result, or throw.

Fixes #50

Type of Change

Use an x in between the [ ] for each line applicable to the type of change for this PR

• Bug fix
• New Feature
• Documentation
• Code improvement
• Breaking change - if a public API changes, or any change that DOES or MAY require a major revision to the NuGet package version due to semver.
• Unit tests
• Code samples
• Added your repository URL to the readme because you make use of this super cool package! ;)
• Other

Describe testing that was performed for your change

New unit tests against cancellation token support

• Can return a value as handling for cancellation
• Can throw as handling for cancellation

Checklist

• Read the https://github.com/OrleansContrib/Orleans.SyncWork/blob/main/CONTRIBUTING.md
• Ran unit tests and ensured they passed
• Added unit tests where applicable
• Referenced an issue where applicable
• Ran dotnet-format locally

[Kritner]

This unfortunately is a breaking change in that the original abstract method to be implemented:

protected abstract Task<TResult> PerformWork(TRequest request);

has been changed to:

protected abstract Task<TResult> PerformWork(
  TRequest request, GrainCancellationToken grainCancellationToken);

This should be a minimally breaking change, but it is a breaking change nonetheless.

Not totally sure what to do regarding breaking changes in relationship to package versioning, since a breaking change warrants a major version increment, but was trying to keep the major version in line with the Orleans version... :X

[Kritner]

Added some info and a poll to #54.

Don't know if it will get any responses since not really sure who is using the package, but will at a minimum wait a while to hear feedback.