Implement non-mapped async IO for CUDA on Windows. (#7896)

Implement non-mapped async IO for CUDA on Windows.  (#7896)

* Implement non-mapped async IO for CUDA on Windows. On a fast Gen5 NVMe drive this change improves model load time by >3x while it should be the same (or slightly faster) on any other drive.

* Free resources except for backend.

* Change assertions to exceptions in llama_file, find correct cuda backend to create CUDA resources and respect the use_mmap flag again for CUDA.

* Apply suggestions from code review

Co-authored-by: slaren <redacted>
* Fix editorconfig and unused variable

* Fix issues with Windows build

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Co-authored-by: slaren <redacted>