Nixica 0.5.0 downstream rollout

Summary

Track updating all downstream consumers to nixica 0.5.0 (includes flake.lib lazy attrs from !13 (merged)).

Consumer MRs

• horizon-flake-parts
• hackage-server-module
• haskell-make-package-set
• horizon-supported-systems
• ghc-common-hadrian
• werrorwolf
• nixlab
• agent-roster

@smartypants is updating these now.

Follows from #4 (closed) (0.4.0 rollout, now closed).