Feature multiple primary keys and cleanup

[devkral]

Changes Linting:

• format with ruff line length 120 (before there was an inconsistent limit to line length 99)
• don't set explicit the wrong line length

Big Changes:

• multiple primary keys are now supported
• add to_python
• global constraints
• don't set attributes three times (model) only 2 times (validation, overwrite dict)

Changes from commit

• add to_python
• replace __set__ with to_python and advise against __set__ (can have bad side-effects)
• allow multiple primary keys (ForeignKeys not supported yet to such models)
• global constraints
• pk is now a reserved field
• compositeField have a redirect mode for primary keys
• fix: alias always None
• fix: spelling

TODO:

• cleanup
• more tests
• ForeignKeys with multiple primary columns
• fix TODOs
• remove embedded_fields_initialized workaround
• add test for ManyToMany's Related Manager is not provided on object

[devkral]

This is required as base for the further development. The linting changes can be cherry picked, it was accidentally that I found out that the settings differ

[devkral]

I need some help with the TODOs

[devkral]

merge as base? Or wait for the foreign keys to work and some TODOs resolved

[tarsil]

Lets point to release @devkral and complete the changes