fix(provider-generator): emit provider functions into a "functions" submodule - #400

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: hashicorp/setup-copywrite@32638da2d4e81d56a0764aa1547882fc4d209636. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/