chore: update nextjs v15, react v19 and eslint v9 (#420)

.changeset/swift-donuts-own.md

helpers/typescript.ts

templates/types/streaming/express/eslint.config.mjs

templates/types/streaming/express/eslintrc.json

templates/types/streaming/express/index.ts

templates/types/streaming/express/package.json

...s/types/streaming/nextjs/app/api/files/[...slug]/route.ts

templates/types/streaming/nextjs/next.config.json

templates/types/streaming/nextjs/package.json

templates/types/streaming/nextjs/tsconfig.json