feat: add meaningful errors

[ntn-x2]

Fixes https://github.com/KILTprotocol/ticket/issues/2552, by both removing all occurrences of .expect() and .unwrap() and replacing them with Internal errors, and by introducing error enums. The logic is that for both the provider and the consumer, a generic error is bubbled up from the runtime, and because of the constraints imposed by Substrate, the error reason is encoded as a u16, where each "class" of error is namespaced with a 255 value increment. A snippet of this is shown below:

fn from(
    value: DipSiblingProviderStateProofVerifierError<
        ParachainHeadMerkleProofVerificationError,
        IdentityCommitmentMerkleProofVerificationError,
        DipProofVerificationError,
        DidSignatureVerificationError
    >,
) -> Self {
    match value {
        DipSiblingProviderStateProofVerifierError::ParachainHeadMerkleProofVerificationError(error) => {
            error.into()
        }
        DipSiblingProviderStateProofVerifierError::IdentityCommitmentMerkleProofVerificationError(error) => {
            u8::MAX as u16 + error.into() as u16
        }
        DipSiblingProviderStateProofVerifierError::DipProofVerificationError(error) => {
            u8::MAX as u16 * 2 + error.into() as u16
        }
        DipSiblingProviderStateProofVerifierError::DidSignatureVerificationError(error) => {
            u8::MAX as u16 * 3 + error.into() as u16
        }
    }
}

The specific reason for the error can then be retrieved and decoded directly from the Polkadot Apps interface, as the example below shows, where the first byte 01 indicates the enum variant index, the second byte is the varint encoding of the SCALE-encoded u16, and the third and forth bytes e000 represent the u16 error reason. This can be decoded as decimal, where each value has a one-to-one link to a specific error from the runtime.

The pallet consumer expects any other implementation of the DIP consumer protocol to expose the proof verification error reason as a u16, but of course developers are free to not give any meaning to it and treat everything as a generic InvalidProof error.

[ntn-x2]

Merging without reviews. It will be reviewed later on from the aa/dip branch directly.