Weakdeps tryout
Shouldn't be merged for now – demonstrates stdlib weakdeps issues.
If @devmotion or others with a better understanding of weakdeps can resolve these warnings you see in CI, they are welcome!
Not sure from which side (Julia or packages), but those weakdeps issues are somehow getting resolved: new CI runs show no warnings or errors about them without any changes here.
The only remaining strange thing is the type instability in getall on Julia 1.6. Behavior on that version shouldn't be affected by this PR at all...
Oh, it was just a wrong version! Now indeed we have no errors/warnings with this PR and can finally make the last dep weak. Anyone against this?