pytato_array_context changes (#216)

* adds meshmode.Pytato_Array_Context

Co-authored-by: Matthias Diener <mdiener@illinois.edu>

* simple-dg: take --lazy to use PytatoPyOpenCLArrayContext

Co-authored-by: Matthias Diener <mdiener@illinois.edu>

* avoid naming collision b/w variable and function name

Co-authored-by: Matthias Diener <mdiener@illinois.edu>

* test with arraycontext.git@pytato

* add lazy simple-dg test

* correct path

* add pytato to requirements.txt

* fix test

* PytatoArrayContext is available on main

* [not working] Cache codegen result in freeze()

* Revert "[not working] Cache codegen result in freeze()"

This reverts commit dd976214be03bb751e946d940d9b5c017e70762e.

* Draft: two-actx simple-dg

* fix the 2-actx

* remove unused code

Co-authored-by: Kaushik Kulkarni <kaushikcfd@gmail.com>
Co-authored-by: Andreas Kloeckner <inform@tiker.net>