…key generation

Replace the custom 64-bit non-cryptographic combined DJB2 hashing implementation in HttpTransferCache with a robust, pure JavaScript, synchronous SHA-256 algorithm.

Using DJB2 is vulnerable to pre-image and second-preimage attacks due to its small 64-bit keyspace and mathematical simplicity. An attacker could craft colliding request inputs to poison the cache, potentially causing a CDN or the application to serve the wrong cached response to legitimate users.

SHA-256 provides strong cryptographic collision resistance, preventing cache key collision attacks. A custom synchronous implementation is required because the Web Crypto API (`crypto.subtle.digest`) is asynchronous, whereas the transfer cache state lookup and interceptor flow must operate synchronously.

Also, update the unit tests to dynamically verify the custom SHA-256 output against the native Web Crypto API.