I don't really love how the features are laid out inside receive especially. Send is not as big of a deal because the state machine has been flattened. If there were separate modules for separate features I think they'd be easier to reason about from docs.rs

Consider removing the not(feature = v2) feature since we want to discourage its use and one can replicate v1 soverignty by running both a directory and payjoin client on the same machine. Rust features should be additive.

• separate send::{v1, v2} modules Abstract send feature error variants into separate feature-specific abstractions #464
• Fix PjUriBuilder feature mess Separate receive submodules to be additive #466
• Place receive v1 typestate machine into receive::v1 module with feature-gated visibility
• Separate receive::{v1, v2} errors (related: Review usage of crate::receive::Error #312,) Separate receive::{v1,v2} error modules #482
• set optional_parameters::SUPPORTED_VERSIONS according to calling module, not feature flag #490

follow ups:
#500