On Windows, recent llama.cpp changes make mmap slower in most cases, so default to off. This also implements a tri-state for use_mmap so we can detect the difference between a user provided value of true/false, or unspecified.
--------- Co-authored-by: Patrick Devine <patrick@infrahq.com>
--------- Co-authored-by: Chris-AS1 <8493773+Chris-AS1@users.noreply.github.com>