Replace tiny-keccak with sha3::Keccak256

[0xh3rman]

Summary

• Remove tiny-keccak direct dependency, use sha3::Keccak256 which was already a dependency
• Add hex to gem_hash
• Add keccak256 unit test

Test plan

• cargo clippy -p gem_hash -- -D warnings passes
• just test gem_hash passes

[gemini-code-assist]

Code Review

This pull request replaces the tiny-keccak dependency with sha3 in the gem_hash crate, simplifies the keccak256 implementation, and adds unit tests. It also updates the socket2 dependency version across the workspace. Feedback suggests improving the unit tests by comparing raw byte arrays instead of hex-encoded strings to enhance performance and clarity.