v0.12.0 release

[LLFourn]

• Add SharedKey::from_non_zero_poly
• Add SharedKey::grind_fingerprint method
• Add ShareImage type
• Add FROST_V0_FINGERPRINT export
• Change poly::scalar::to_point_poly to make it less opinionated
• Add From/TryFrom conversions for Scalar to all unsigned integer types
• Add Shamir secret sharing helpers for scalar polynomials
• Upgrade to bincode v2
• MSRV 1.63 -> 1.85
• Refactor CompactProof in sigma_fun to use two type parameters CompactProof<R, L> instead of CompactProof<S: Sigma> to enable serde support
• Update secp256kfun_arithmetic_macros to use generic NonZero<T> type instead of NonZeroU32
• Add hash-to-curve methods to Point:
  • hash_to_curve - Simple try-and-increment with uniform distribution (recommended)
  • hash_to_curve_sswu - RFC 9380 compliant constant-time hashing
  • hash_to_curve_rfc9381_tai - RFC 9381 VRF try-and-increment format
• Add Message::new for BIP340-compliant domain separation using 33-byte padded prefix
• Deprecate Message::plain which uses non-standard 64-byte prefix
• Remove type parameters from Message and Signature types (always public now)
• Remove unused Slice type from secp256kfun
• SharedKey::check_fingerprint now returns Option<usize> instead of bool, indicating number of bits verified
• Rename PartyIndex to ShareIndex
• Fix from_bytes_uncompressed to validate points are on curve
• Add vrf_fun crate
• Point<_, _, Zero> implements Hash
• Add VRF-based certification for certpedpop
• Make certpedpop signature scheme configurable