devcontainer: drop common-utils feature

The MS Go devcontainer image (2.1-1.26) already ships the vscode user,
sudo, git, curl, zsh, oh-my-zsh, etc. The common-utils feature re-runs
the same install (visible as a 2-min apt-get against deb.debian.org)
for no behavioral change. Removing it cuts cold-start from ~3min to ~30s.

Author: css521

.devcontainer/.features.temp.dockerfile

@@ -0,0 +1,19 @@
+FROM mcr.microsoft.com/devcontainers/go:2.1-1.26
+COPY --from=jb-devcontainer-features-762b7b096d19fd5170c4177074e82d13 /tmp/jb-devcontainer-features /tmp/jb-devcontainer-features/
+ENV PATH="/usr/local/share/nvm/current/bin:/usr/local/go/bin:/go/bin:/go/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+ENV GOLANG_VERSION="1.26.4"
+ENV GOTOOLCHAIN="local"
+ENV GOPATH="/go"
+ENV GOROOT="/usr/local/go"
+ENV NVM_DIR="/usr/local/share/nvm"
+ENV NVM_SYMLINK_CURRENT="true"
+ENV _CONTAINER_USER="root"
+ENV _CONTAINER_USER_HOME="/root"
+ENV _REMOTE_USER="vscode"
+ENV _REMOTE_USER_HOME="/home/vscode"
+
+USER root
+RUN chmod -R 0755 /tmp/jb-devcontainer-features/ghcr.io-devcontainers-features-common-utils-2 \
+&& cd /tmp/jb-devcontainer-features/ghcr.io-devcontainers-features-common-utils-2 \
+&& chmod +x ./devcontainer-feature-setup.sh \
+&& ./devcontainer-feature-setup.sh

.devcontainer/devcontainer.json

@@ -16,14 +16,16 @@
     "--security-opt=apparmor=unconfined"
   ],
 
-  "features": {
-    "ghcr.io/devcontainers/features/common-utils:2": {}
-  },
-
+  // No `features` block: the MS Go devcontainer image already ships the
+  // vscode user, sudo, git, curl, zsh, oh-my-zsh, and everything else
+  // common-utils would have installed — adding the feature just re-runs
+  // a 2-minute apt-get for nothing (and stalls behind deb.debian.org on
+  // slow networks).
+  //
   // libbtrfs-dev lets you build with `-tags btrfs` (the optional fast-path
   // backend that needs cgo); the default static build needs nothing.
-  // sudo: devcontainer lifecycle commands run as remoteUser (vscode), not root.
-  // The common-utils feature gives vscode passwordless sudo.
+  // `sudo` because lifecycle commands run as remoteUser (vscode), and the
+  // base image's vscode user has passwordless sudo configured.
   "postCreateCommand": "sudo apt-get update && sudo apt-get install -y -qq libbtrfs-dev make",
   // Show the Makefile target list every time the container is attached, so a new
   // contributor immediately sees what they can do (build / test / verify / demo).