Swap out hpke-spec for hpke-rs

[jvmncs]

CAPE-820

• rewrites all of the existing functionality to use hpke-rs as our rust backend.
• breaking change: rename the python library to hybrid_pke
• breaking change: renames hpke_open -> open and hpke_seal -> seal
• breaking change: hpke-rs puts the functions generate_key_pair, open, and seal directly on the Hpke configuration struct, so in Python-land these are no longer pure functions but rather instance methods on the python class binding to Hpke
• breaking change: expands the signatures of open/seal to include info, aad, and optional psk, psk_id, and pk_s/sk_r
• exposes the underlying hpke_rs::HpkeError enum as a set of custom python Exceptions through PyO3, which significantly improves the experience of handling Rust errors from Python