fix: remove usage of Buffer from top-level

Author: Shubham Chaturvedi

modules/cache-material/src/build_cryptographic_materials_cache_key_helpers.ts

@@ -15,16 +15,15 @@ import {
 } from '@aws-crypto/serialize'
 import { compare } from './portable_compare'
 
-//  512 bits of 0 for padding between hashes in decryption materials cache ID generation.
-const BIT_PAD_512 = Buffer.alloc(64)
-
 export function buildCryptographicMaterialsCacheKeyHelpers<
   S extends SupportedAlgorithmSuites
 >(
   fromUtf8: (input: string) => Uint8Array,
   toUtf8: (input: Uint8Array) => string,
   sha512: (...data: (Uint8Array | string)[]) => Promise<Uint8Array>
 ): CryptographicMaterialsCacheKeyHelpersInterface<S> {
+  //  512 bits of 0 for padding between hashes in decryption materials cache ID generation.
+  const BIT_PAD_512 = Buffer.alloc(64)
   const sorting: SerializeOptions = { utf8Sorting: true }
   const { serializeEncryptionContext, serializeEncryptedDataKey } =
     serializeFactory(fromUtf8, sorting)