Add ARM64 (aarch64) target support

[khamutov]

First off — thank you for maintaining these Rust bindings to Dokany. We've been running dokan-rust in production on Windows ARM64 machines for about six months, carrying a small local patch to make it build there, and we'd like to upstream that change so it's maintained here rather than living in our fork.

dokan-sys panics at build time on any target architecture other than x86/x86_64. So cargo build --target aarch64-pc-windows-msvc fails today, even though Dokany ships ARM64 binaries and the v2.3.0 installer provides an ARM64 import library. This PR adds the aarch64 → ARM64 mapping in check_dokan_env, so dokan-sys/dokan build for Windows on ARM64.

Validated on a native Windows-on-ARM64 machine with Dokany v2.3.0 installed:

• cargo build --release --workspace --all-targets succeeds. Before this change the same command panics with Unsupported target architecture!.
• The Dokan kernel driver mounts and responds correctly on ARM64 (the usage_tests exercise it against a real volume).