Update to JSpecify

[jevanlingen]

What's changed?

Replace OpenRewrite NonNull with JSpecify's variant.

What's your motivation?

Deprecation fix 😉

Checklist

• [x] I've added unit tests to cover both positive and negative cases
• [x] I've read and applied the recipe conventions and best practices
• [x] I've used the IntelliJ IDEA auto-formatter on affected files