Refactor custom project parsing so Python models have dedicated method

[tatiana]

In order to implement support to Python models in #375 we reused some existing methods from the legacy Project codebase to support Python models when using LoadMode.CUSTOM. The goal with this ticket is to refactor the code so we have adequate code coverage and Python models are parsed with a dedicated method, and not _handle_sql_file, as discussed in:
#375 (comment)

[dosubot]

Hi, @tatiana. I'm Dosu, and I'm helping the Cosmos team manage their backlog. I wanted to let you know that we are marking this issue as stale.

From what I understand, you opened this issue suggesting a refactoring of the custom project parsing in order to have a separate method for parsing Python models. This would avoid reusing existing methods. However, there hasn't been any activity or comments on the issue since then.

Could you please let us know if this issue is still relevant to the latest version of the Cosmos repository? If it is, please comment on the issue to let the Cosmos team know. Otherwise, feel free to close the issue yourself, or the issue will be automatically closed in 7 days.

Thank you for your understanding and contribution to the Cosmos repository.