feat(build_npm.ts): add importMap to build script

The build script for npm has been updated to include an importMap. This
change allows for better control over the import paths used in the
build process.

Author: ryoppippi

scripts/build_npm.ts

@@ -15,6 +15,7 @@ await build({
   typeCheck: false,
   test: false,
   entryPoints: ["src/index.ts"],
+  importMap: "./import_map.json",
   outDir: "./npm",
   shims: {
     deno: "dev",