test: add missing implementation-plan test targets

tests/bundle_test/verify_external_shape.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+rule_file="$1"
+build_file="$2"
+
+grep -Eq 'for package in ctx\.attr\.external:' "${rule_file}"
+grep -Eq 'args\.add\("--external"\)' "${rule_file}"
+grep -Eq 'name = "external_bundle"' "${build_file}"
+grep -Eq 'external = \["left-pad"\]' "${build_file}"