bug(felt): Felt is not zeroized on drop

[Trantorian1]

Bug Report

types-rs version: 7ef3023

Current behavior: Felt does not implement any zeroizing when it is dropped, opening the door for potential memory read attacks on sensitive information such as private keys.

Expected behavior:

Felt should implement #[derive(ZeroizeOnDrop)] or similar to allow memory zeroing when dropped. This could be feature-gated.

Given Felt is currently based on lambdaworks-math FieldElement, and this does not implement any zeroing logic, either a manual implementation using ptr::write_volatile and atomic::compiler_fence or an update to lambdaworks-math would be needed.

A relevant issue has been opened there as well.

Other information:

While there certainly are more common ways to leak sensitive cryptographic information like private keys, it seems like for something in our control such as in-memory representation we should at least provide this as an option.