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/lib.rs

@@ -6,3 +6,15 @@ pub mod package_info;
 pub mod pull;
 
 pub type ProgressCallback<'a> = Option<&'a dyn Fn(&str, &str, usize, usize)>;
+
+/// Returns the architecture of current CPU, debian-compatible
+pub fn get_current_arch() -> String {
+    match std::env::consts::ARCH {
+        "x86" => "i386".to_string(),
+        "x86_64" => "amd64".to_string(),
+        "arm" => "armhf".to_string(),
+        "aarch64" => "arm64".to_string(),
+        "powerpc64" => "ppc64el".to_string(),
+        x => x.to_string(),
+    }
+}