CI is slower than it needs to be

[dlqqq]

Problem

The current CI pipeline takes at least 15 minutes to complete given all checks pass. This can be seen from the workflow runs on #136.

I believe that the CI is running slower than it needs to because there are unnecessary dependencies between jobs. This can be seen in the following excerpt from .github/workflows/build.yml, which I've abbreviated for clarity:

jobs:
  build_jupyter-chat:
    ...
  test_extensions:
    name: Python unit tests (Python ${{ matrix.python-version }})
    runs-on: ubuntu-latest
    needs: build_jupyter-chat
    ...
  integration-tests:
    name: Integration tests
    needs: build_extension
    runs-on: ubuntu-latest

The integration-tests job is one of the slowest jobs in the pipeline, and it doesn't start until test_extensions passes, which in turn doesn't start until build_jupyter-chat passes.

I don't see an obvious benefit to keeping the inter-job dependencies that exist today. One may argue that this reduces runner usage, but this is only true when the CI fails (which is ideally <<50% of the time). One may also argue that this results in seeing fewer failed jobs when the CI fails, but again, this is optimizing for failure.

Proposed Solution

Remove the needs field from all jobs, and allow the CI to run fully in parallel.