chore: swap argument order in `cfc` and `cfcₙ`

[j-loreaux]

trafficstars

This changes the argument order for cfc and cfcₙ from cfc (a : A) (f : R → R) to cfc (f : R → R) (a : A). This has a few advantages:

1. It's closer to the usual reading (cfc f a vs. f(a) on paper).
2. argument order looks better for cfc_comp (cfc (g ∘ f) a = cfc g (cfc f a) instead of cfc a (g ∘ f) = cfc (cfc f a) g).
3. it will be much easier to speak of operator convexity and monotonicity if we can just write cfc f.

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