Force device scalars on PyOpenCLArrayContext (#43)

* add a flag to force device scalars on the CL array context

* remove local pylintrc from meshmode

* parametrize tests for force_device_scalars

* add docs for force_device_scalars

* add proper typing hints to _loopy_transform_cache

* use np.isscalar instead of isinstance(Number)

* fix type hints for _loopy_transform_cache

* use specific type in _kernel_name_to_wait_event_queue

* add pytest_generate_tests_for_array_context

* add env var to select array context for tests

* fix mypy issues

* add a documented PytestArrayContextFactory

* update test generator to return a closure

* add a way to register factories as strings

* actually fix the implementation

* fix doc formatting

* better names for global variables

* move norm to BaseFakeNumpyLinalgNamespace

* simplify and deduplicate pytest fixture setup