Fix struct cast panic in rule and add tests

[connortsui20]

Summary

Closes: #6933

Testing

Adds a regression test as well as a few other tests to confirm this is correct.

[codspeed-hq]

Merging this PR will improve performance by 18.36%

⚡ 2 improved benchmarks
✅ 1007 untouched benchmarks
⏩ 1515 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	bitwise_not_vortex_buffer_mut[1024]	535.6 ns	477.2 ns	+12.22%
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	376.1 ns	317.8 ns	+18.36%

---

_{Comparing ct/struct-cast-rule (2cdbd3c) with develop (8ac7234)}

Footnotes

1. 1515 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩