Make ServiceInvoker async

[acodrington]

Description

This PR adds a InvokeAsync method to IServiceInvoker and ServiceInvoker, as part of [sc-53211]. This allows the ServiceInvoker to invoke async implementations of services with sync interfaces.

Upon succesfully acquiring a lease from the IServiceFactory, InvokeAsync will search for an async method on the registered service which matches the name of requested method, but also follows these conventions:

• Must end with Async
• Must have a CancellationToken as its last argument
• Must return either Task or Task<T>, depending on whether the originally requested method returns void or a result.

This feature is dependant on the implementation of IServiceFactory being used (Octopus Server and Tentacle use their own implementations), but we can now register async implementations of sync services in the DelegateServiceFactory:

var serviceFactory = new DelegateServiceFactory();
serviceFactory.Register<IMySyncService, IMyAsyncService>(() => new MyAsyncServiceImpl());

In the above example, there is no formal relationship between IMySyncService and IMyAsyncService, but the async interface must replicate the sync interface whilst adhering to the conventions listed above.

The DelegateServiceFactory will throw an exception upon registration if the async interface does not follow the conventions, via the new AsyncServiceVerifier helper class.

Main changes:

• Add async code path to IServiceInvoker
• Add AsyncServiceVerifier for verifying the mapping between sync and async service interfaces.
• Add tests for ServiceInvoker and AsyncServiceVerifier
• Fixed bug in sync code of ServiceInvoker, where method lookup could fail if params array was null rather than empty
• Added overload method DelegateServiceFactory to allow registering async implementations against a sync service interface, and verify that mapping conforms to conventions.
• Added additional internal method to DelegateServiceFactory for purposefully registering non-comforming sync/async service interfaces (used in testing)

Related to https://github.com/OctopusDeploy/Issues/issues/8266

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #53211: 🎉 🎉 🎉 Make Halibut Support Async RPC Calls 🎉 🎉 🎉.

[LukeButters]

The description I think should give an example of the behaviour that this PR adds e.g. an example around how an async service can be supplied and called as well as some details around how it has to be done/what the methods need to look like etc.