refactor: make pedersen vk fields public

[lighterabc]

Description

This PR makes pedersen.VerifyingKey fields (G and GRootSigmaNeg) public to be able to read/copy at gnark/std/recursion/groth16/verifier.ValueOfVerifyingKey

Type of change

How has this been tested?

How has this been benchmarked?

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[CLAassistant]

All committers have signed the CLA.

[ivokub]

Perfect! Thanks for the contribution!