feat: Add process package to monorepo

- Add `sal-process` package for cross-platform process management.
- Update workspace members in `Cargo.toml`.
- Mark process package as complete in MONOREPO_CONVERSION_PLAN.md
- Remove license information from `mycelium` and `os` READMEs.

os/README.md

@@ -98,7 +98,3 @@ if is_linux() {
     print("Running on Linux");
 }
 ```
-
-## License
-
-Licensed under the Apache License, Version 2.0.