Fix shortcomings in YAML/Python data models

[igorlukanin]

Cube supports YAML for data modeling as well as Python and Jinja for data modeling and configuration. However, there are a few shortcomings that we'd like to address to ensure great developer experience:

• {cube.sql()} is not supported in YAML/Python #7484
• Allow to import Python files from cube.py #8443
• { in sql would not allow the data model to compile #8250
• Rollup Designer in Cube Core is broken for YAML data models #5989
• Incomplete data model validation: an array is accepted as time_dimension in a pre-aggregation definition #9138
• Incomplete data model validation: strings are accepted in the list of dimensions in a pre-aggregation definition #9137

It's currently planned for May 2025.