Refactor: move hash helper to util.js and extract metadata functions into metadataUtil.js

[Copilot]

Consolidates the hash utility alongside other general helpers and separates metadata/matcher concerns into a dedicated module.

Changes

• src/util.js — Added hash (DJB2, previously private to ReadablePartition); removed createHmac, matches, buildMetadataForMatcher, buildMatcherFromMetadata, and the crypto import.
• src/metadataUtil.js (new) — Houses all metadata builder/matching functions: createHmac, matches, buildMetadataForMatcher, buildMatcherFromMetadata.
• src/Partition/ReadablePartition.js — Drops local hash definition; imports hash from ../util.
• src/Storage/ReadableStorage.js / src/Storage/WritableStorage.js — Updated imports to pull metadata functions from ../metadataUtil.

// Before: hash was a private function in ReadablePartition.js
// After:
const { hash } = require('../util');

// Before: metadata functions lived in util.js
// After:
const { createHmac, matches, buildMetadataForMatcher, buildMatcherFromMetadata } = require('../metadataUtil');

[coveralls]

coverage: 98.121% (+0.002%) from 98.119%
when pulling c832a66 on copilot/move-hash-helper-to-utils
into 22c0088 on main.