v1.16: [zk-token-sdk] Make ElGamalKeypair fields private (backport of #32190)

[mergify]

This is an automatic backport of pull request #32190 done by Mergify.
Cherry-pick of 1452ed7 has failed:

On branch mergify/bp/v1.16/pr-32190
Your branch is up to date with 'origin/v1.16'.

You are currently cherry-picking commit 1452ed704.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   programs/zk-token-proof-tests/tests/process_transaction.rs
	modified:   zk-keygen/src/main.rs
	modified:   zk-token-sdk/src/encryption/elgamal.rs
	modified:   zk-token-sdk/src/encryption/grouped_elgamal.rs
	modified:   zk-token-sdk/src/instruction/batched_grouped_ciphertext_validity.rs
	modified:   zk-token-sdk/src/instruction/ciphertext_ciphertext_equality.rs
	modified:   zk-token-sdk/src/instruction/ciphertext_commitment_equality.rs
	modified:   zk-token-sdk/src/instruction/grouped_ciphertext_validity.rs
	modified:   zk-token-sdk/src/instruction/pubkey_validity.rs
	modified:   zk-token-sdk/src/instruction/transfer/with_fee.rs
	modified:   zk-token-sdk/src/instruction/transfer/without_fee.rs
	modified:   zk-token-sdk/src/instruction/withdraw.rs
	modified:   zk-token-sdk/src/instruction/zero_balance.rs
	modified:   zk-token-sdk/src/sigma_proofs/batched_grouped_ciphertext_validity_proof.rs
	modified:   zk-token-sdk/src/sigma_proofs/ciphertext_ciphertext_equality_proof.rs
	modified:   zk-token-sdk/src/sigma_proofs/ciphertext_commitment_equality_proof.rs
	modified:   zk-token-sdk/src/sigma_proofs/grouped_ciphertext_validity_proof.rs
	modified:   zk-token-sdk/src/sigma_proofs/pubkey_proof.rs
	modified:   zk-token-sdk/src/sigma_proofs/zero_balance_proof.rs
	modified:   zk-token-sdk/src/zk_token_elgamal/decryption.rs
	modified:   zk-token-sdk/src/zk_token_elgamal/ops.rs

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   programs/zk-token-proof/benches/verify_proofs.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[codecov]

Codecov Report

Merging #32235 (5a7035c) into v1.16 (ba76e34) will decrease coverage by 0.1%.
The diff coverage is 97.0%.

❗ Current head 5a7035c differs from pull request most recent head 2ac06f6. Consider uploading reports for the commit 2ac06f6 to get more accurate results

@@            Coverage Diff            @@
##            v1.16   #32235     +/-   ##
=========================================
- Coverage    81.9%    81.9%   -0.1%     
=========================================
  Files         760      761      +1     
  Lines      207432   207494     +62     
=========================================
+ Hits       169952   169971     +19     
- Misses      37480    37523     +43