Fix Windows build with --no-default-features

[danbugs]

Fixes #685 and updates CI to ensure Windows builds successfully without default features.

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Btw, to validate this fix, I tested running Nanvix (which uses --no-default-features) on Windows as a guest. This revealed that additional register setup was needed in hyperv_windows.rs:

• Mirror the CS register setup used with default features, except without the L bit
• Explicitly set the Limit parameter for CS to 0xFFFF (required when paging isn't initialized)

These changes ensure Windows Hyper-V properly initializes guest VMs that don't use the init-paging feature.

[ludfjig]

Looks good! I think we should strive to set the same registers on all hypervisors, so we don't rely on any inherent defaults of a particular hv. Thoughts?

[danbugs]

Looks good! I think we should strive to set the same registers on all hypervisors, so we don't rely on any inherent defaults of a particular hv. Thoughts?

Probably a good idea—we should also avoid relying on Default and be a little more explicit. For example, on KVM, the default CS register (excluding base & selector fields) looks like this:

CS: limit=0xffff, type=0xa, s=1, dpl=0, p=1, avl=0, l=0, db=0, g=0

This is exactly the setup we needed w/o default-features to run a workload like Nanvix and why it worked from the get go. But, on WHP, Default just zeroes out everything :|

Might be a good work item for #469?

[syntactically]

Does this change need to be mirrored on the Linux hypervisor drivers?

[syntactically]

Should we also be checking that compilation with a hypervisor driver but without init-paging succeeds on Linux?