chore: Replace internal.js shim with explicit export

[davidkna-sap]

1. Remove the internal.js shims which can cause issues with swc and move to dedicated export map.
2. To still support /nested/imports where necessary add conditional exports (INTERNAL_ONLY/export/name) tied to a new workspace condition and enable in project tsconfig and jest
3. This required adjusting jest mocking
4. This also required moving to more recent moduleResolutions
5. As ncc does not support conditions, move to rolldown (configured via test-util package helper)
6. Configure rolldown to rewrite __filename and __dirname to import.meta.*, removing the need for excluding these from the bundle with nested imports.
7. Disable prettier on generated .github/actions to avoid slowdown

Closes https://github.com/SAP/ai-sdk-js-backlog/issues/576

[marikaner]

[q] What is INTERNAL_ONLY?

[davidkna-sap]

For any exported files that requires the workspace condition (not importable directly by third party packages, afaik even transitively), I added this so it's easier to spot in diffs so it does not end up in any of the non-test production code.

[marikaner]

I read up on this. Really nice! What I don't like though, is that you have to import it using "INTERNAL_ONLY". Wouldn't it be nicer to export everything like (aka. directly) this for tests?
I would expect something along the lines of:

 ".": {
      "types": "./dist/index.d.ts",
      "default": "./dist/index.js",
      "workspace": {
        "types": "./internal.ts",
        "default": "./internal.ts"
      }
    },
  "./test/test-util/create-generator-options": {
      "workspace": {
        "types": "./test/test-util/create-generator-options.ts",
        "default": "./test/test-util/create-generator-options.ts"
      },

I am not even sure you can configure it this way and it would be ok to consider something like this a follow up.

[davidkna-sap]

It doesn't need to have that prefix, but I wanted to make it very visible as tests will also have the condition enabled; and I wanted to ensure that it's not ever imported in production code.