Currently, the tests added in rapidsai#27 (backported to 24.04 in rapidsai#36) do not
check the exit codes of their subprocesses. This means that failing
tests are not caught. This PR fixes the test utilities to check the exit
codes and print any stdout/stderr outputs.

This PR makes a number of significant changes to the patching infrastructure:
1. This PR reorganizes the patching logic to be based on a more principled approach. Rather than maintaining lists of patch functions that are each responsible for filtering modules to apply themselves to, patches are organized in the patches directory in a tree structure matching dask itself. Patches are found and run by importing the same relative paths within the `patches` directory corresponding to a particular dask or distributed module.
2. It adds proper support for patching submodules. Previously the loader was being disabled whenever a real dask module was being imported, but this is problematic because if some dask modules import others they will pre-populate `sys.modules` with the real modules and therefore the loader will never be used for loading a patched version of the submodule.
3. Patches are no longer just functions applied to modules, they are arbitrary functions executed when a module is imported. As a result, a wider range of modifications is possible than was previously allowed. In particular:
4. The more general functions allow the entire module import to be hijacked and redirected to other modules.
5. The new framework is used to vendor a patched version of the accessor.py module in dask, which resolves the issues observed in dask/dask#11035.

Authors:
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Richard (Rick) Zamora (https://github.com/rjzamora)

URL: rapidsai#39