v6.6.1

Upgrade priority: Low. Internal maintennce updates.

Changes:

• Fix construction for palletVersion keys with correct prefix
• Add Polkadot EthereumAddress as a known PortableRegistry override
• De-dupe PortableRegistry namespace splitting operations
• Optimize internal AbstractArray & Struct u8a decoding
• Shortcut Struct construction from Struct instance
• Use internal lookupName in createClass (allows deeply recursive lookups)
• Codec toHex() will now correctly return the TS HexString type
• Update known upgrade blocks for Westend & Kusama
• Bump static metadata for latest Substrate, Polkadot & Kusama