Fix code scanning alert no. 2: Insecure randomness

[gnongsie]

Fixes https://github.com/AuthorizeNet/sdk-node/security/code-scanning/2

To fix the problem, we need to replace the use of Math.random() with a cryptographically secure random number generator. In Node.js, the crypto module provides a secure way to generate random values. Specifically, we can use crypto.randomBytes to generate secure random bytes and then convert these bytes to the required format.

1. Replace the Math.random() calls in test/utils.js with crypto.randomBytes.
2. Ensure that the generated random values are converted to the appropriate format (e.g., integers or strings).

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