move ViewsFromSequences from Python to C++ and simplify unit tests

modules/base/src/CMakeLists.txt

modules/base/src/export_helper/pair_to_tuple_conv.hh

modules/gfx/pymod/export_entity.cc

modules/seq/base/pymod/__init__.py

modules/seq/base/pymod/export_sequence.cc

modules/seq/base/src/CMakeLists.txt

modules/seq/base/src/sequence_handle.cc

modules/seq/base/src/sequence_handle.hh

modules/seq/base/src/views_from_sequences.cc

modules/seq/base/src/views_from_sequences.hh

modules/seq/base/tests/test_seq.py