Add style warning, or interpreter optimization, for `first select`

[bkDJ]

I've seen some uiua videos on YouTube where people do the sort idiom select rise dup, but they only want the first item so they follow up with first. What do you think about prodding them in the right direction with a style guideline, or having the interpreter perform the fastest possible calculation for a given end result.

Values ← ⌊×1e9 [⍥⚂1e6]

⍜now(⊢⊏⍖.) Values
⍜now(⊡⊢⍖.) Values
⍜now(/↥) Values

The time difference is 2 orders of magnitude apart.

[kaikalii]

This has been added in 563d98bb94b86b0cd9f3.