Fix lvalue arguments in coroutine cleanup helpers

[fallintoplace]

What

• Allow lvalue arguments in coroutine cleanup helpers.

Why

• at_coroutine_exit(action, value) fails to compile. Its wrapper returns __task<int&>, but the coroutine creates __task<int>.

Implementation

• Decay argument types in both cleanup wrapper return types.

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[ericniebler]

/ok to test 5654a84

[ericniebler]

thanks!