Repackaging

[sgwilym]

Re-organises the exported modules of both willow-data-model and meadowcap.

willow-data-model

• willow_data_model::encoding has benefitted the most, with everything pulled up into the willow_data_model::encoding namespace, and all synchronous equivalents in willow_data_model::encoding::sync.
• What was previously in willow_data_model::entry is now in the root module.
• What was previously in willow_data_model::path is now in the root module.
• What was previously in willow_data_model::parameters is now in the root module.
• No nested modules in willow_data_model::grouping, now everything has been pulled up into that module.

meadowcap

• Everything has been moved to the root module.
• There is now a dedicated SubspaceDelegation struct.

Other

Renamed the willow-data-model-fuzz crate to just willow-fuzz.