Add decaf448 support

[daxpedda]

This PR adds support for decaf448 based on RustCrypto/elliptic-curves#1121.

• Update MSRV to v1.85 and edition to 2024 because elliptic-curve` & co. betas require it.
• Update elliptic-curve & co. to v0.14.0-rc.1. It will still take a while for all these dependencies to release a stable version, see Tracking issue for next release series RustCrypto/traits#1571.
• Add Decaf448 and implement CipherSuite and Group. This also adds the decaf448 and decaf448-ciphersuite crate feature.
• Expand CipherSuite with type ExpandMsg, now that we aren't just using expand_message_xmd, but also expand_message_xof. This also gets rid of a some constraints on CipherSuite and Group that where only relevant for ExpandMsgXmd.
• Change the hash output constraint from 256 bytes to u16::MAX, the only real constraint set upon the hash size by the protocol: https://www.rfc-editor.org/rfc/rfc9497#section-2.2.1-5. I2OSP(len(seed), 2), the seed is a hash output, which would fail if its length doesn't fit into a u16 here.
• Constrain Group::ElemLen with IsLess<U65536>, which gets rid of a potential runtime error, that is now moved to compile time.

Based on #140.

[daxpedda]

Split MSRV bump off in #140.