add Sealed to introspection traits

[luxedo]

Part of #3908

Adds Sealed to traits in impl_/retrospection.rs

[davidhewitt]

Thanks for catching! Probably need to have a custom Sealed trait here unique to this trait, e.g. see extract_argument.rs.

[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 luxedo:3908/seal-introspection (d08f573) 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. ↩