Add Windows ARM bindings

[CGMossa]

Fixes #190

Current status: This is compiling, but it is not producing the right result as none of the machine are Windows ARM machines, and thus, don't have the right Rtools (with the right Rust) installed.

[yutannihilation]

Sorry, I didn't know it's this tricky.

https://github.com/r-rust/faq#does-rust-support-windows-on-arm64-aarch64

[CGMossa]

Rust doesn't ship with std binaries for these. Somehow, this https://doc.rust-lang.org/cargo/reference/unstable.html#build-std needs to be part of the CI for these new targets.
I have not figured out this.

[CGMossa]

Status: What's missing are the appropriate headers. They must be.. somewhere. If someone wants to take over, please do! I'll give this a break for now.

[CGMossa]

They are here:

if (ARCH == "arm64") {
    core.addPath(`C:\\rtools44-aarch64\\usr\\bin`);
    core.addPath(`C:\\rtools44-aarch64\\aarch64-w64-mingw32.static.posix\\bin`);
 }

mingw variable needs to be corrected to this, when on Windows+Arm

[CGMossa]

Okay, while this may compile. It isn't actually installing Rtools with ARM, or anything like that yet.

[CGMossa]

Closing in favor of #267.

AI-written details

This PR's cross-compile approach predates the bindgen detach (#250): build.rs no longer has a generate_bindings path and the artifact-emit CI it relied on has been removed, so it can no longer produce a bindings file in-tree. #267 takes the now-viable route instead, regenerating natively on a windows-11-arm runner (GA 2025-08-07) by pinning the last pre-detach generator, with the layout tests run on-target rather than skipped.

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Drafted by Claude (claude-opus-4-8). Reviewed by the author.