Replace "may" with "might" to avoid ambiguity

[jeffreyesun]

As written, "Non-mutating functions may also use mutation under the hood" might imply that non-mutating functions are allowed to use mutation under the hood

[Please delete this text and describe your change here.
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PR Checklist

• Tests are added
• Documentation, if applicable

[ToucheSir]

I wonder if that note shouldn't be reworded to be even clearer (e.g. spell out what "non-mutating" means and how this includes functions the user may not even be aware of deep in the bowels of some (standard) library. Until that happens though, this seems like a reasonable change.