* import and update BlockIndexRanges from sumpy

* move make_block_index to utils

* add a test for the cartesian product of matrix indices

* port uses of BlockIndexRanges to new versions

* point requirements to wip sumpy branch

* fix some small doc issues

* Point sumpy back to main in req.txt

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* fix some array context mismatching

* only freeze cached DISCRETIZATION scoped expressions

Improve proxy generator

* Use TransformationRemover

* Use itgt to index targets

* src->sources, tgt->targets

* Use sumpy wip branch

* Fix typo

* Fix center_itgt->itgt

* Fix LayerPotentialOnTargetAndCenterSubset to use targets

* pass itgt_name

* Remove whitespace on blank line

* Fix get_optimized_kernel

* sdr, tdr -> sxr, txr

* Point req.txt for sumpy back to main

Co-authored-by: Andreas Klöckner <inform@tiker.net>

Matrix evaluation updates

That's where all the geometry is cached, so we might as well
reuse it.

https://github.com/inducer/modepy/pull/38#issuecomment-846472970

* update examples to use arraycontext

* update tests to use arraycontext

* update pytential to use arraycontext

* update call to num_reference_derivative

* restore PyOpenCLArrayContext annotations

Drop symengine version requirement in .test-conda-env-py3.yml

* Update install instructions

* Clarify miniforge instructions

* Use improved miniforge link from @isuruf