fix: cache-buster hash is always 6 characters - #188

Fixes #187

getHash converts the crc32 to hex without padding. When the crc32 has leading zeros (about 1 in 16 inputs), the hex string has an odd length, Buffer.from(hex, 'hex') drops the last digit, and the hash comes out 4 characters long instead of 6. Below 0x10 the hash is empty.

Changes

• getHash pads the hex to 8 digits before decoding it.
• A test in test/core/Utils.test.ts covers crc32 values with 1, 2 and 3 leading zero digits, and checks that hashes without a leading zero are unchanged. The test fails before the fix (expected 'n6td' to match /^[\w-]{6}$/) and passes after it.

Hashes that were already 6 characters don't change. Only files whose crc32 starts with a zero get renamed, once. In the Manifest tests this renames sprite-sDtC@0.5x.png, sprite-3CLG.webp and the spine textures. tps-Ktro9A-0@0.5x.png.json, dragon-VMxv5A@0.5x.atlas and dragon-672U@0.5x.webp.atlas change too, because they reference renamed textures, so their expected names are updated.

npm run test:lint and npm run test:types pass.

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