feat: added untagged enum support

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.83660% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.73%. Comparing base (c27e3a8) to head (4d76b86).

Files	Patch %	Lines
Sources/MacroPlugin/Plugin.swift	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #78 +/- ## ========================================== + Coverage 94.50% 94.73% +0.23% ========================================== Files 101 108 +7 Lines 3385 3707 +322 ========================================== + Hits 3199 3512 +313 - Misses 186 195 +9 ```

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