refactor(zk_verifier): reuse HashToField from cometbls/crypto/bn254

[Himess]

This PR removes the locally defined HashToField function in zk_verifier.go and instead reuses the implementation provided in the cometbls repository under:

• https://github.com/unionlabs/cometbls/blob/960ce8b37bd94347cd17dd4dbed18159a2855520/crypto/bn254/bn254.go#L194

The function was already defined and exported in the bn254 module, so duplicating it locally was unnecessary.

Changes:

• Removed the local HashToField function from zk_verifier.go
• Replaced it with comet.HashToField from github.com/unionlabs/cometbls/crypto/bn254
• Verified that the behavior and logic match the original

Closes #2804

[vercel]

@Himess is attempting to deploy a commit to the unionbuild Team on Vercel.

A member of the Team first needs to authorize it.