v9.12.1

Changes:

• Add isStorageFallback on the Codec interface. (true if entry was created from a metadata fallback value from an empty storage item)
• Ensure api.queryMulti returns empty result when no keys are provided
• Add explicit Array checks on Vec/Tuple inputs
• Align Struct.{toU8a/toPrimitive/toHuman/toJSON} population of results
• Apply memoization to batched API queries
• Update to latest Polkadot, Kusama & Substrate metadata