test: add missing implementation-plan test targets

tests/bun_test_test/cache_hit_shape.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+rule_file="$1"
+
+grep -Eq 'set -euo pipefail' "${rule_file}"
+grep -Eq 'src_args = " "\.join' "${rule_file}"
+grep -Eq 'exec "\$\{bun_bin\}" test \{src_args\} "\$@"' "${rule_file}"