fix __qualname__ for complex enum variants

[davidhewitt]

Closes #5788

This adds a __qualname__ field to the generated complex enum variant classes.

It might be nice to eventually refactor the macros to do this without so much boilerplate. This'll do for shipping 0.28.1.

[codspeed-hq]

Merging this PR will improve performance by 18.8%

⚡ 1 improved benchmark
✅ 98 untouched benchmarks
⏩ 1 skipped benchmark¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	format_simple	368.6 ns	310.3 ns	+18.8%

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_{Comparing davidhewitt:complex-enum-qualname (07243dd) with main (5338c48)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩