Generalise topology to take multiple cell types (#2979)

* Add b ack some mixed topology

* Start working on mixed topology again

* Create _entity_types instead of _cell_type

* Fixes in Python for testing

* A bit of debug and a test

* Add access to IndexMaps

* Add more accessors and tests

* Use general version of create_topology

* Clarify for mypy

* Add more accessors and test

* Use nb::overload_cast

* Remove commented code

* Add test file

* more tests

* Improve docs

* Const fix

* const fix

* Doc fix

* Use int8_t

* more int8

* flake8

* More suggestions

* Fixes for suggestions

* flake8

* Apply suggestions from code review

Co-authored-by: Jørgen Schartum Dokken <[email protected]>

* Add a few suggestions

* Update cpp/dolfinx/mesh/Topology.cpp

Co-authored-by: Jørgen Schartum Dokken <[email protected]>

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Co-authored-by: Jørgen Schartum Dokken <[email protected]>