Ok but... JSON allows "\/" to mean "/".  Dumb that it does, but it does.  If you find a "\\/"  that means "\/".  The "\\" prefix becomes "\" and the suffix remains "/".  The escaping is not recursive so it then remains "\/" in total, it doesn't do another pass to become "/".

But it probably doesn't matter much.  Events that use "\/" escaping are kinda dumb and unnecessary and NIP-01 violations.

As for things like scientific notation, I never expected any relays to support that. Chorus doesn't. The test is just more of a curiousity.  This is why it says "NO" meaning NO we don't support that (perhaps stupid) thing, rather than the more judgemental FAIL.