feat: prepare reth Signature migration to alloy

[leruaa]

Motivation

To achieve https://github.com/paradigmxyz/reth/issues/10750 and replace reth Signature type by alloy one,

Solution

The following is needed:

• impl Default for Parity
• impl Hash and Default for Signature
• add as_hex_bytes() and size() to Signature

I also moved some unit tests from reth to alloy.

PR Checklist

• [x] Added Tests
• [ ] Added Documentation
• [ ] Breaking changes