Some `Smul`s in code

Stream: mathlib4

[Jihoon Hyun]

The current master branch contains Smul in following files:
Mathlib/Data/Set/Pointwise/SMul.lean
Mathlib/Data/Rat/Cast.lean
Mathlib/Algebra/Module/Basic.lean
Mathlib/Tactic/ToAdditive.lean -- This seems irrelevant
If these Smuls should be changed to SMul, I'll make a pull request for that.
Also, I'd like to check, if SMul appears in front of the theorem, which of sMul_xx or smul_xx is correct?

[Mario Carneiro]

SMul is the correct name, and smul is how it is spelled in theorems

[Mario Carneiro]

(the rule is that if there is a cluster of capitals at the beginning of the name, they are all lowercased together)