Small clean-up of notebook processing code.

[Bubblyworld]

See #93.

Preparing the code for two changes to come: 1) Moving away from import statement parsing and towards explicit requirements. 2) Consistent way of handling backend config requirements. We have a bunch of hacky code for k8s docker repo secrets and aml config at the moment, and every backend is going to need stuff like this.

[github-actions[bot]]

Unit Test Results

  1 files    1 suites   31s :stopwatch: 62 tests 50 :heavy_check_mark: 12 :zzz: 0 :x:

Results for commit 87c03fd6.