feat(file): add context manager to File

[msnyder5]

Summary

Add a context manager to nextcord.File. This will automatically call close() on the file when the context manager exits scope.

Also change force_close to be optional default to None so that we can set force_close to True when using context manager if False was not provided to init.

Old Method

file = nextcord.File(filepath)
await channel.send(file=file)
file.close()

New Method (w/ Context Manager)

with nextcord.File(filepath) as file:
    await channel.send(file=file)

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
  • I have run task pyright and fixed the relevant issues.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed) Edit: This actually isn't a breaking change as you can still use the old syntax.
• This PR is not a code change (e.g. documentation, README, ...)

[ooliver1]

Nice first PR, thanks for the explanation!

[ooliver1]

Did not need to make that approved.

[EmreTech]

Not tested.

[alentoghostflame]

Haven't tested but it LGTM!