Replace libsecp256k1 with k256 in FRAME related code (#10883)

* Replace libsecp256k1 with k256 in beefy-mmr

* Port of FRAME `contracts` benchmarking from `libsecp256k1` to `k256`

* Newtype to allow `Pcg32` rng usage with `k256` in contracts benchmarks

* Use `sp-io::crypto` to generate dummy keys in `contracts` bechmarks

* More compact code

* Cargo fmt

* Build `sp-keystore` only for dev profile

* Move public key generation back to the `map`