feat: split executor and reader

[pd93]

Currently, Task's Executor does everything. In some ways this keeps things simple as you only have to initialise one thing, but in other ways it makes things much more difficult as it essentially creates one giant black box with a single input and output. Our tests tend to encompass the entire process, from reading a file to parsing and merging it, to executing it and checking the output.

This PR starts to break out components of the executor into smaller chunks that are more easily undestandable and testable. The first items is the Reader. Next, will be the formatter which is a precursor to working on #2091.

One side effect of this change is that the package API surface increases slightly and a lot of our tests need to be fixed as a result. However, I think this also has the benefit of making it easier to understand what is actually happening when using the task package.

• refactor: split executor and reader
• refactor: merge Setup into NewExecutor
• feat: remove entrypoint from the executor
• fix: executor and formatter tests
• feat: test wildcards