feat: oci packer can now use mksquashfs if available (#70)

* feat: oci packer can now use mksquashfs if available

* fix: use nproc in kernel build script for default jobs, and fix DEV.md guide

* feat: working erofs backend

Cargo.lock

@@ -1517,11 +1517,13 @@ dependencies = [
  "backhand",
  "bytes",
  "env_logger",
+ "indexmap 2.2.6",
  "krata-tokio-tar",
  "log",
  "oci-spec",
  "path-clean",
  "reqwest",
+ "scopeguard",
  "serde",
  "serde_json",
  "sha256",