4 fix api deprecations (#7)

* Migrate code from Python 2 to Python 3 syntax

* First round of typing error fixes

* Fix regressions from last commit

* Remove deprecated coreapi, removed in DRF 3.17.0

* Fix more PyLance errors

* removate.json weekly-update -> minor-update

* Update src/rest_flex_fields2/serializers.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/rest_flex_fields2/views.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/rest_flex_fields2/utils.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/copilot-instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update doc/CHANGELOG.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fix copilot warnings

* Fix copilot errors

* Update src/rest_flex_fields2/serializers.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/tests/test_flex_fields_model_serializer.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>