Document type-piracy / type-leakage restrictions for `require_stdlib` (#56005)
I was a recent offender in
https://github.com/JuliaLang/Pkg.jl/issues/4017#issuecomment-2377589989
This PR tries to lay down some guidelines for the behavior that stdlibs
and the callers of `require_stdlib` must adhere to to avoid "duplicate
stdlib" bugs
These bugs are particularly nasty because they are experienced
semi-rarely and under pretty specific circumstances (they only occur
when `require_stdlib` loads another copy of a stdlib, often in a
particular order and/or with a particular state of your pre-compile /
loading cache) so they may make it a long way through a pre-release
cycle without an actionable bug report.