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.

src/builder/state.rs

@@ -0,0 +1,89 @@
+//! Build state tracking to allow resuming interrupted builds.
+
+use anyhow::Result;
+use serde::{Deserialize, Serialize};
+use std::collections::HashSet;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum BuildStep {
+    PatchesApplied,
+    PostExtractDone,
+    Configured,
+    PostCompileDone,
+    PostInstallDone,
+}
+
+#[derive(Debug, Default, Serialize, Deserialize)]
+struct State {
+    completed_steps: HashSet<BuildStep>,
+}
+
+pub struct StateTracker {
+    state_file: PathBuf,
+    state: State,
+}
+
+impl StateTracker {
+    pub fn new(source_dir: &Path) -> Result<Self> {
+        let state_file = source_dir.join(".depot_state");
+        let state = if state_file.exists() {
+            let content = fs::read_to_string(&state_file)?;
+            toml::from_str(&content).unwrap_or_default()
+        } else {
+            State::default()
+        };
+
+        Ok(Self { state_file, state })
+    }
+
+    pub fn is_done(&self, step: BuildStep) -> bool {
+        self.state.completed_steps.contains(&step)
+    }
+
+    pub fn mark_done(&mut self, step: BuildStep) -> Result<()> {
+        self.state.completed_steps.insert(step);
+        self.save()
+    }
+
+    fn save(&self) -> Result<()> {
+        let content = toml::to_string_pretty(&self.state)?;
+        fs::write(&self.state_file, content)?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+
+    #[test]
+    fn test_state_tracker_init() -> Result<()> {
+        let dir = tempdir()?;
+        let tracker = StateTracker::new(dir.path())?;
+        assert!(!tracker.state_file.exists());
+        Ok(())
+    }
+
+    #[test]
+    fn test_mark_done_and_persistence() -> Result<()> {
+        let dir = tempdir()?;
+        let mut tracker = StateTracker::new(dir.path())?;
+
+        assert!(!tracker.is_done(BuildStep::Configured));
+        tracker.mark_done(BuildStep::Configured)?;
+        assert!(tracker.is_done(BuildStep::Configured));
+
+        // Check file exists
+        assert!(tracker.state_file.exists());
+
+        // Reload
+        let tracker2 = StateTracker::new(dir.path())?;
+        assert!(tracker2.is_done(BuildStep::Configured));
+        assert!(!tracker2.is_done(BuildStep::PostCompileDone));
+
+        Ok(())
+    }
+}