feat: Add KeychainError

[lewie9021]

This PR includes:

• Added a custom KeychainError error class
• Added a fix similar to ci: fix e2e #767 to get the CI checks passing

This is mostly a follow on from #762 and looks to make it easier for consumers to identify errors from this library and provide type safety when responding to various error codes:

import Keychain, { KeychainError, ERROR_CODE } from "react-native-keychain";

Keychain.getGenericPassword()
  .catch((err) => {
    if (err instanceof KeychainError) {
      console.log('Retry error?', err.retryable);

      switch (err.code) {
        case ERROR_CODE.AUTH_CANCELED:
          console.log('Authentication was canceled');
          break;
        case ERROR_CODE.BIOMETRIC_TIMEOUT:
          console.log('Biometric prompt timed out');
          break;
        case ERROR_CODE.BIOMETRIC_LOCKOUT:
          console.log('Too many failed attempts, biometric authentication locked');
          break;
        default:
          console.log(`Keychain error: ${err.code} - ${err.message}`);
      }
    }
  })

If there's interest, I'd be happy to extend the KeychainError class with static methods that can help for cases where only specific error handling is required:

import Keychain, { KeychainError } from "react-native-keychain";

Keychain.getGenericPassword()
  .catch((err) => {
    if (KeychainError.isAuthCanceledError(err)) {
      return console.log('Authentication was canceled');
    }

    console.log(`Error: ${err.message}`);
  })