Resolve Windows SDK ucrt path dynamically in build.rs

[Copilot]

The Windows debug build was pinned to a single Windows SDK version via a hardcoded MSVC_PATH, which breaks when only newer SDKs are installed. This updates build.rs to resolve the ucrt library path dynamically instead of assuming 10.0.22000.0.

• Windows SDK path resolution

  • replace the fixed SDK path with runtime resolution in build.rs
  • prefer an explicit MSVC_PATH override when provided
  • otherwise use standard Windows SDK environment variables if present
  • fall back to scanning Windows Kits\\10\\Lib and selecting the newest SDK that contains ucrt/x64

• Build-script invalidation

  • add rerun-if-env-changed entries for the Windows SDK-related environment variables so Cargo rebuilds when the configured SDK path changes

• Focused build-script coverage

  • add small unit tests for SDK version normalization and latest-SDK selection logic

if let Some(path) = env::var_os("MSVC_PATH") {
    let path = PathBuf::from(path);
    if has_windows_ucrt_libs(&path) {
        return Some(path);
    }
}

find_latest_windows_sdk_dir(Path::new(WINDOWS_KITS_LIB_DIR))

• Fixes Add dynamic MSVC_PATH for ucrt #12

[1337-42]

LGTM