[zk-sdk] Change FeeSigmaProof to PercentageWithCapProof (#1084)

* rename submodule `fee` with `percentage_with_cap`

* rename `FeeSigmaProof` type to `PercentageWithCapProof`

* rename `FeeMaxProof` and `FeeEqualityProof` with `PercentageMaxProof` and `PercentageEqualityProof`

* remove `fee` from the variable names

* remove `fee` from function names

* rename `FeeSigmaProofVerificationError` to `PercentageWithCapVerificationError`

* flatten out function arguments

* update docs/comments

* update test names

* clippy

zk-sdk/src/sigma_proofs/errors.rs

@@ -39,9 +39,9 @@ pub struct ZeroCiphertextProofVerificationError(#[from] pub(crate) SigmaProofVer
 impl_from_transcript_error!(ZeroCiphertextProofVerificationError);
 
 #[derive(Error, Clone, Debug, Eq, PartialEq)]
-#[error("fee sigma proof verification failed: {0}")]
-pub struct FeeSigmaProofVerificationError(#[from] pub(crate) SigmaProofVerificationError);
-impl_from_transcript_error!(FeeSigmaProofVerificationError);
+#[error("percentage-with-cap proof verification failed: {0}")]
+pub struct PercentageWithCapProofVerificationError(#[from] pub(crate) SigmaProofVerificationError);
+impl_from_transcript_error!(PercentageWithCapProofVerificationError);
 
 #[derive(Error, Clone, Debug, Eq, PartialEq)]
 #[error("public key validity proof verification failed: {0}")]