fix(deps): eliminate next-compose-plugins

Next.js v15 supports next.config.ts file, and there you will get an error about next-compose-plugins does not have `@types/next-compose-plugins`, so to not create file types with `declare module ...` for this specific problem it's easier to replace all the meaning of compose plugins with just a single `reduce` function.

detailed explanation here:
https://github.com/hashicorp/next-mdx-enhanced/issues/18#issuecomment-859196106

package.json

@@ -50,7 +50,6 @@
     "class-variance-authority": "^0.7.0",
     "lodash": "^4.17.21",
     "next": "^14.2.3",
-    "next-compose-plugins": "^2.2.1",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "tailwind-merge": "^2.3.0",