fix: check for guild for role processors

[AstreaTSS]

Pull Request Type

• Feature addition
• Bugfix
• Documentation update
• Code refactor
• Tests improvement
• CI/CD pipeline enhancement
• Other: [Replace with a description]

Description

This PR fixes role processors from erroring out when the guild cache is limited or made NullCache. Previously, the processors assumed the guild would always exist, when this isn't always the case.

Worth noting: many more processors use a fetch_guild to work around this. That... isn't a good idea here, as if the guild isn't in the cache, we likely don't care about it at all.
(Honestly, many processors could benefit from switching from fetch_guild to get_guild, but that would be breaking.)

Changes

See the diff.

Related Issues

Test Scenarios

• Disable guild cache.
• Create or delete a role.

Python Compatibility

• I've ensured my code works on Python 3.10.x
• I've ensured my code works on Python 3.11.x

Checklist

• I've run the pre-commit code linter over all edited files
• I've tested my changes on supported Python versions
• I've added tests for my code, if applicable
• I've updated / added documentation, where applicable

[silasary]

yay, edge case scenarios!