✨ Feature: Blog post on the difference between 'assertion' and 'cast'

[JoshuaKGoldberg]

Feature Request Checklist

• I have searched for related issues and found none that matched my issue.
• This is the appropriate issue form for the feature I would like to request.

Feature

I mention in the book that common use of the two terms are different:

• Assertion commonly means a type-system only operation: we're "asserting" that, regardless of inference, a value is a particular type
• *Cast8 commonly means a runtime change: we're casting/coercing a value at runtime to a different value

This gets confused a lot. IMO it'd be helpful to have an article.

Additional Info

Inspired by @kirkwaiblinger's typescript-eslint/typescript-eslint#10458, thank you Kirk! 😄

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