feat: Implement build state tracking and interactive package specification creation

- Added StateTracker to manage build steps and allow resuming interrupted builds.
- Updated post_extract function to utilize StateTracker for patch and command execution.
- Introduced makefile.rs to handle building and installing packages via Makefile.
- Created interactive.rs for an interactive package specification creator with SHA256 computation for source URLs.
- Enhanced checksum verification to support multiple algorithms (SHA256, SHA512, MD5).
- Added example configuration files in contrib for system-wide and user-level Depot configurations.
- Updated tests to cover new functionality and ensure correctness of state tracking and interactive creation.

contrib/README.md

@@ -0,0 +1,20 @@
+Contrib: example system and user configuration files for Depot
+
+Place these files on your system to provide sensible defaults and examples
+for `/etc/depot.toml`, `/etc/depot.d/build.toml`, or user-level configs.
+
+Recommended installation:
+
+  # System-wide
+  sudo cp contrib/depot.toml /etc/depot.toml
+  sudo mkdir -p /etc/depot.d
+  sudo cp -r contrib/depot.d/* /etc/depot.d/
+
+  # Per-user (example)
+  mkdir -p ~/.config
+  cp contrib/user.depot.toml.example ~/.config/depot.toml
+
+Notes
+ - These files are examples only. Review and adapt to your distribution and
+   security policies before deploying.
+ - The config loader supports append syntax (e.g. `cflags += ["-g"]`).