replace some `|Num.floor _|%N with Num.trunc _

[pi8027]

Motivation for this change

#1244 (comment)

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

Reminder to reviewers

• Read this Checklist
• Put a milestone if possible
• Check labels

[affeldt-aist]

Just add the lemma to the changelog and we are good to go.

[pi8027]

Please merge #1415 first.

[proux01]

@pi8027 why is this still a draft? Could you please rebase, add the four entries to the changelog and we merge.

[proux01]

Done, will merge when CI is happy

[pi8027]

why is this still a draft?

Because I didn't have time to extensively perform this change and separate orthogonal changes (e.g., divrr -> divff) to another PR (or another commit at least).

[proux01]

Ok, the current state of the PR is already an improvement, so let's merge it as it is. Any further change can come in a subsequent PR indeed.