deb: cross-compilation, ephemeral contexts, local builds

Multiple changes:
- New contexts (schroot, unshare)
- Cross-building quirks, with ephemeral contexts and repositories management
- Contexts with parents, global context manager, better lifetime handling
- Local building of binary packages
- Pull: pulling dsc files by default
- Many small bugfixes and changes

Co-authored-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Co-committed-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>

src/deb/sbuild.rs

@@ -0,0 +1,35 @@
+/// Sbuild binary package building
+/// Call 'sbuild' with the dsc file to build the package with unshare
+use crate::context;
+use std::error::Error;
+
+pub fn build(
+    package: &str,
+    _version: &str,
+    arch: &str,
+    series: &str,
+    build_root: &str,
+    cross: bool,
+) -> Result<(), Box<dyn Error>> {
+    let ctx = context::current();
+    let mut cmd = ctx.command("sbuild");
+    cmd.current_dir(format!("{}/{}", build_root, package));
+    cmd.arg("--chroot-mode=unshare");
+    cmd.arg("--no-clean-source");
+
+    if cross {
+        cmd.arg(format!("--host={}", arch));
+    } else {
+        cmd.arg(format!("--arch={}", arch));
+    }
+    cmd.arg(format!("--dist={}", series));
+
+    // Add output directory argument
+    cmd.arg(format!("--build-dir={}", build_root));
+
+    let status = cmd.status()?;
+    if !status.success() {
+        return Err(format!("sbuild failed with status: {}", status).into());
+    }
+    Ok(())
+}