Make curve25519 and bn128 out into their own crates

[samkim-crypto]

Problem

The curve25519 code contains logic related to curve25519 syscalls. It is currently contained in zk-token-sdk create, but is mostly independent of the rest of the (token) logic in the crate. There are some downstream projects that only require the curve25519 logic, but unnecessarily need to depend on the entire set of dependencies in zk-token-sdk.

This is also the case with bn128 logic in the solana-program crate as it is independent of the rest of the logic there.

Proposed Solution

Separate out these crates into their own separate crates:

• curve25519 (Extract curve25519 crate from zk-token-sdk #951)
• bn128