feat: Add support for new OS package

- Add a new `sal-os` package containing OS interaction utilities.
- Update workspace members to include the new package.
- Add README and basic usage examples for the new package.

os/src/lib.rs

@@ -0,0 +1,13 @@
+pub mod download;
+pub mod fs;
+pub mod package;
+pub mod platform;
+
+// Re-export all public functions and types
+pub use download::*;
+pub use fs::*;
+pub use package::*;
+pub use platform::*;
+
+// Rhai integration module
+pub mod rhai;