feat: add phase 7 bun_install module extension

tests/install_extension_test/extension_shape_test.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+extension_file="$1"
+
+grep -q 'bun_install = module_extension(' "${extension_file}"
+grep -q 'tag_classes = {"install": _install}' "${extension_file}"
+grep -q '"package_json": attr.string(mandatory = True)' "${extension_file}"
+grep -q '"bun_lockfile": attr.string(mandatory = True)' "${extension_file}"