[!348] Changes after code generation profiling

Merge branch 'feature/profiling' into 'master'

ref:extensions/dune-codegen I am poking through performance bottlenecks in
order to speed up code generation. This always boils down to memoization of
expensive function calls.

This fixes [#74].

See merge request [extensions/dune-codegen!348]

  [#74]: gitlab.dune-project.org/NoneNone/issues/74
  [extensions/dune-codegen!348]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/348


Closes #74