Support Windows & Fix warnings

[vaqxai]

Summary

• Fixes Windows build by gating Unix-specific permission APIs and cleaning up platform warnings.
• Clarifies PyO3 lifetime annotations to silence mismatched lifetime warnings.

Changes

• Added conditional compilation for Unix-only PermissionsExt usage and permission checks, with Windows-safe fallbacks.
• Removed unused Windows metadata variables behind cfg to avoid unused warnings.
• Normalized PyO3 return signatures to use explicit '_ lifetimes for Cow<[u8]> in bindings, resolving lifetime syntax warnings.

Testing

cargo build --release on Windows (msvc)
maturin develop --release after installing maturin

[basfroman]

We don't officially support Windows OS. We currently don't have the capacity to fully develop, test, and support Wallet for Windows OS. However, we've separated the Rust and Python code in the current version, and you might be able to build without any additional changes.