Invert meaning of operator bool for CUDA stream and event

[msimberg]

This was a leftover from #190. See #190 (comment).

[msimberg]

I see also that there actually already sort of existed a cudaEvent_t wrapper... just hidden inside the future helper. I'll try to unify the event wrapper added in #190 with the existing one in a separate PR.

[Copilot]

Pull request overview

This PR aligns the boolean conversion semantics of CUDA stream/event wrappers with typical C++ “valid object == true” expectations (and with the GHEX_C_STRUCT / GHEX_C_MANAGED_STRUCT behavior referenced in the linked #190 discussion), by making moved-from objects evaluate to false.

Changes:

• Invert operator bool() for ghex::device::stream and ghex::device::cuda_event to return true when the wrapper is usable (not moved-from).
• Update the event_pool internal assertion to match the new cuda_event boolean semantics.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
include/ghex/device/cuda/stream.hpp	stream::operator bool() now reports validity (!m_moved).
include/ghex/device/cuda/event.hpp	cuda_event::operator bool() now reports validity (!m_moved).
include/ghex/device/cuda/event_pool.hpp	Adjust assertion in get_event() to reflect the new cuda_event truthiness.

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[msimberg]

I see also that there actually already sort of existed a cudaEvent_t wrapper... just hidden inside the future helper. I'll try to unify the event wrapper added in #190 with the existing one in a separate PR.

I opened #200.