feat: Infer ScheduledEvent.entity_type

[zachnieto]

Summary

Infer ScheduledEvent.entity_type from provided Channel type when creating ScheduledEvent #590

Checklist

• [X] If code changes were made, then they have been tested
  • [X] I have updated the documentation to reflect the changes
  • [X] I have formatted the code properly by running task lint
  • [X] I have type-checked the code by running task pyright
• [ ] This PR fixes an issue
• [X] This PR adds something new (e.g. new method or parameters)
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[zachnieto]

This looks good.

Shiftinv mentioned the idea of adding these changes to GuildScheduledEvent.edit(), would you like to make those in this pull as well, or would you rather this is a second pr? Either is fine, you can even open the second pr if you'd like.

Might as well do it all here !

[zachnieto]

First time doing overloads in python, hopefully im getting close lol