fix for windows

[jeanwsr]

Fix Windows support for dynamic library loading.

• PATH separator: : on Unix/macOS, ; on Windows.
• CONDA_PREFIX Windows library paths: on Windows, also searches {CONDA_PREFIX}/Library/bin and {CONDA_PREFIX}/Library/lib (in addition to the existing {CONDA_PREFIX}/lib).
• LIB_NAME_LINK SO version: "s-dftd3-1" on Windows to match the conda MinGW shared library libs-dftd3-1.dll. The -1 SO version may need updating if upstream bumps ABI.
• DLL_PREFIX: hardcoded "lib" on Windows since std::env::consts::DLL_PREFIX returns "" for all Windows targets regardless of toolchain, but MinGW convention uses the lib prefix.

Fully written by DeepSeek V4 Pro based on fully human analysis of the problem.

[jeanwsr]

The fix is based on what i see after failure on windows, but I don't have an instant way to test it since all windows build is not local. Maybe we could just blind check and publish a crate for test.