feat: Enhance service manager with zinit socket discovery and systemd fallback

- Improve Linux support by automatically discovering zinit sockets
  using environment variables and common paths.
- Add fallback to systemd if no zinit server is detected.
- Enhance README with detailed instructions for zinit usage,
  including custom socket path configuration.
- Add example demonstrating zinit socket discovery.
- Add logging to show socket discovery process.
- Add unit tests for service manager creation and socket discovery.

service_manager/Cargo.toml

@@ -36,6 +36,7 @@ rhai = ["dep:rhai"]
 tokio-test = "0.4"
 rhai = { workspace = true }
 tempfile = { workspace = true }
+env_logger = "0.10"
 
 [[test]]
 name = "zinit_integration_tests"