Use `sealed` where possible

In .NET 6, there were many performance improvements made to marking classes as `sealed`. [Microbenchmarks show somewhere between 2x to 500x performance improvement][1].

This may require #455 to be completed first.

[1]: https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-6/#peanut-butter

The issue does not name any files, tests, or entry points; first check the status of prerequisite issue #455 and identify the classes in component-detection that can be sealed. Use the linked .NET 6 performance guidance for context. Done means eligible classes are marked sealed without breaking the project's existing validation.

Written by the indexing model from the issue text.