refactor(executor): Check custom visit functions in #[derive(Visit)]

[dima74]

Description

While working on #4599, I noticed that in custom executor it is possible to derive Visit with invalid #[visit(custom())] functions which will be ignored (only rustc error that function is unused). This PR adds check for custom visit function names to avoid potential bugs. Also I updated documentation of some proc-macros related to custom executor.

#[derive(Constructor, ValidateEntrypoints, Validate, Visit)]
#[visit(custom(visit_register_domain2))]  // typo in visit_register_domain
struct Executor {
    verdict: Result,
    block_height: u64,
}
fn visit_register_domain(...) { ... }

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Checklist

• I've read CONTRIBUTING.md
• I've used the standard signed-off commit format (or will squash just before merging)
• All applicable CI checks pass (or I promised to make them pass later)
• (optional) I've written unit tests for the code changes
• I replied to all comments after code review, marking all implemented changes with thumbs up