feat(windows): implement icon and string resource loading

- Add IconRc struct for loading icons from executable or .ico files
- Implement LoadIconRcError for icon loading error handling
- Add StrRc struct for loading string resources from files
- Implement LoadStrRcError for string loading error handling
- Remove old Icon struct and related error types
- Update tests to use new resource loading implementations
- Add Windows Resource section with proper documentation
- Include Win32_System_LibraryLoader feature in Cargo.toml

wfassoc/Cargo.toml

@@ -13,6 +13,7 @@ windows-sys = { version = "0.60.2", features = [
     "Win32_UI_WindowsAndMessaging",
     "Win32_Security",
     "Win32_System_Environment",
+    "Win32_System_LibraryLoader",
     "Win32_System_Registry",
     "Win32_System_SystemServices",
 ] }