Ensure Date(time) fields are only converted to Nullable when they're not in the primary key

[dlouseiro]

As I reported in this issue, the fact that all Datetime fields are converted to Nullable caused synchronization issues when these fields are part of the table's primary key.

With this PR, I propose that this conversion to Nullable is only done when the field is not part of the table's primary key.

Implementation details:

• Change definition of to_sql_type method not to convert Datetime fields to Nullable by default.
• Create new method to_sql_type_non_primary_key method that ensures Datatime fields are converted to Nullable.
• Change definition of create_empty_table to call to_sql_type_non_primary_key when the field is not part of the primary key, calling to_sql_type otherwise.

While there, formatted the code of connectors.py with ruff formatter to reduce the number of warnings/violations returned by pre-commit. It seems that a lot of other files are also not formatted, but decided to keep the number of non-functional code changes to a minimum.

[dlouseiro]

Hey @BTheunissen , as this is my first PR in this repo and I see you were the one introducing the nullification of datetime fields in this commit, would love your opinion and review here! Thank you