Better sign/verify tests, eddsa support, refactoring of the KeyProvider api

[gasbytes]

This pull request includes several changes to the rustls-wolfcrypt-provider to improve key handling, add support for new algorithms, and clean up the codebase. The most important changes include modifying the key handling for ECDSA keys, adding support for Ed25519, and restructuring the sign module.

Key handling improvements:

• Modified the EcdsaSigningKeyP256Sign, EcdsaSigningKeyP384Sign, and EcdsaSigningKeyP521Sign structures to store private key bytes instead of ECCKeyObject and updated their implementations accordingly (rustls-wolfcrypt-provider/src/sign/ecdsa.rs). [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Support for new algorithms:

• Added support for the Ed25519 algorithm in the sign module and updated the KeyProvider implementation to include Ed25519 (rustls-wolfcrypt-provider/src/lib.rs). [1] [2] [3]

Code restructuring:

• Changed the sign module to make the eddsa submodule public and updated the key handling logic to use closures for defining supported algorithms (rustls-wolfcrypt-provider/src/lib.rs). [1] [2] [3]