[BUG]replace the usage of mviews

[joda9]

Description:
As discussed in #516, the OEP mview tables are no longer supported. Currently, the failing tests are being skipped, but this is not a proper solution. We need to evaluate how to handle the missing data and decide on a long-term approach.

Points to discuss:

• Determine if the data from these mviews is still required.
• Investigate if the same data can be obtained from other tables.
• Assess whether the data is deprecated and can be removed entirely.
• Explore any alternative solutions if needed.

Goal:
Ensure that eDisGo can run without relying on unsupported mview tables and that any necessary data is correctly sourced or replaced.

[joda9]

The legacy Ding0 grid import currently fails.
All oedb_legacy-based generator import tests are affected:

tests/io/test_generators_import.py::TestGeneratorsImportOEDB::test_oedb_legacy_without_timeseries
tests/io/test_generators_import.py::TestGeneratorsImportOEDB::test_oedb_legacy_with_worst_case_timeseries
tests/io/test_generators_import.py::TestGeneratorsImportOEDB::test_oedb_legacy_with_timeseries_by_technology
tests/io/test_generators_import.py::TestGeneratorsImportOEDB::test_target_capacity
tests/test_edisgo.py::TestEDisGo::test_generator_import
tests/test_examples.py::TestExamples::test_edisgo_simple_example_ipynb