chore(deps): upgrade dependency for jf-vrf

[mrain]

closes: #XXXX

This PR:

Upgrade jf-signature dependency to 0.2.0.

• Secret keys are not required to be serde Serializable.

This PR does not:

Key places to review:

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• Targeted PR against correct branch (main)
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added relevant changelog entries to the CHANGELOG.md of touched crates.
• Re-reviewed Files changed in the GitHub PR explorer