Refactor the use of the AutoDownloadStatus enums

[SergioEstevao]

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Fixes #

On this PR we use the enum directly on the model type and avoid the uses of raw value and casting in the codebase. I also found that FMDatabase can support the use of Enum directly on their statements if they are a base type. Ex: Int32, Int, etc..

One of the things that was blocking it was that our base episode protocol was marked as ObjC. I thought there was some reason for the use of @objc tag on the protocols, but after removal I didn't get any kind of error.

If someone knows the reason why those protocols are marked @objc please comment bellow.

To test

• Start the app
• Download some episode
• Check if download status updates are done correctly and reported in the app correctly.
• Check if no crashes or warnings show up in the console.

Checklist

• I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• I have considered adding unit tests for my changes.
• I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[SergioEstevao]

Version 7.79 has now entered code-freeze, so the milestone of this PR has been updated to 7.80.