Add periods to doc comments in modified files

[Copilot]

Addresses review feedback on PR #3127 requesting proper punctuation in documentation comments.

Changes

• algorithms/src/polycommit/sonic_pc/data_structures.rs: Added periods to doc comments for CommitterKey::update(), field descriptions, and utility methods
• algorithms/src/snark/varuna/varuna.rs: Added periods to doc comments for batch_circuit_setup(), prove_vk(), and verify_vk()

Example fix:

// Before:
/// Update the committer_key
/// The `powers_of_beta_g` and `shifted_powers_of_beta_g` may grow or shrink

// After:
/// Update the committer_key.
/// The `powers_of_beta_g` and `shifted_powers_of_beta_g` may grow or shrink.

This PR targets the copilot/pr-3127 branch as part of the stacked PR workflow.

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