Implement and test proper handling of class-side methods, extension methods, trait methods, and special message selectors.

Depends on Traits-eventualUsers.3.cs and complements SUnit coverage for traits.2.cs. [1]

The implementation mostly follows the design of SUnit coverage for traits.2.cs [1], this implementation for smalltalkCI also makes the following changes:
* Moves exclusion of methods derived from traits up from Pharo's overrides of #allClassesToCover to new SCICodeCoverage class>>#cannotBeCovered:
* Moves check for abstract methods from SCICodeCoverage class>>#isExcluded: to SCICodeCoverage class>>#cannotBeCovered:. Consequently, abstract methods will no longer will be displayed as "ignored" but hidden at all from the coverage report.

[1] https://lists.squeakfoundation.org/pipermail/squeak-dev/2022-September/222291.html

…pper

Lol, I had installed an extension that would automatically try to regenerate the TOC upon every save (markdown.extension.toc.updateOnSave) ...