Use zepter to maintain cargo feature hygiene

[clangenb]

This helps to see how features are enabled and propagated. I haven't tested, nor checked it thoroughly, but it might be interesting for us:

https://github.com/ggwpez/zepter

[brenzi]

tested it in encointer/pallets. finds quite a lot and fixes automatically

for pallets:

zepter f f
zepter lint propagate-feature --feature std --workspace --fix
zepter lint propagate-feature --feature try-runtime --workspace --fix
zepter lint propagate-feature --feature runtime-benchmarks --workspace --fix

[brenzi]

hmm, not entirely happy. zepter didn't properly propagate runtime-benchmarks....