Fix for ignored async superstate transitions when child state has unmet guard

[mclift]

This PR is for issue #629 in which a parent state transition is ignored when:

• the child state has a transition configured with the same trigger;
• the child state's transition has an unmet guard condition;
• the parent state's transition does not have unmet guard conditions;
• the child state is the current state;
• the trigger is fired using FireAsync.

When the synchronous call to Fire is used instead, it selects the nearest ancestor that has a transition with no unmet guard conditions.

This PR also includes some housekeeping changes:

• Removed unused #if TASKS directives.
• Changed test method signatures in AsyncFiringModesFixture from void to async Task.
• Split TransitionTests into sync and async test classes.

[Copilot]

Pull Request Overview

This PR fixes an issue where async superstate transitions are ignored when a child state has an unmet guard condition, ensuring consistent behavior between synchronous and asynchronous state machine firing.

• Fixes the async transition handler logic to properly check for unmet guard conditions before falling back to parent state transitions
• Removes unused #if TASKS preprocessor directives throughout the codebase
• Restructures tests by splitting sync and async transition tests into separate classes

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/Stateless.Tests/TransitionTests.cs	Removes async test method and adds comprehensive sync guard condition tests
test/Stateless.Tests/AsyncTransitionTests.cs	New file containing async versions of transition tests to verify the fix
test/Stateless.Tests/AsyncFiringModesFixture.cs	Updates method signatures to async Task and removes unused preprocessor directive
test/Stateless.Tests/AsyncActionsFixture.cs	Removes unused #if TASKS preprocessor directives
src/Stateless/StateRepresentation.Async.cs	Core fix: improves guard condition checking logic in async transition handling
src/Stateless/StateMachine.Async.cs	Removes preprocessor directives and adds missing braces for parameter validation
src/Stateless/StateConfiguration.Async.cs	Removes unused #if TASKS preprocessor directives
src/Stateless/OnTransitionedEvent.cs	Removes unused #if TASKS preprocessor directives

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[mclift]

@MattVane @RedOrc review comments welcomed!

[RedOrc]

Looks good to me :-)

[mclift]

I'll get this merged to dev so a pre-release package gets generated.