Added ability to overflow spell slots with font feature

[vaguely-happy]

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Summary

Here goes a short summary about what the PR is about.

Checklist

PR Type

• [ ] This PR is a code change that implements a feature request.
• [ ] This PR fixes an issue.
• [ ] This PR adds a new feature that is not an open feature request.
• [ ] This PR is not a code change (e.g. documentation, README, ...)

Other

• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] If code changes were made then they have been tested.
• [ ] I have updated the documentation to reflect the changes.
• [ ] I properly commented my code where appropriate