Add Songbird, Coston and Flare

[RareData]

Add support for the EVM-compatible Songbird (canarynet), Coston (testnet) and Flare (mainnet) blockchains. All required details such as RPC endpoints, explorers and chain IDs can be fetched from the ethereum-lists repository:

• Songbird: https://github.com/ethereum-lists/chains/blob/master/_data/chains/eip155-19.json
• Coston: https://github.com/ethereum-lists/chains/blob/master/_data/chains/eip155-16.json
• Flare: https://github.com/ethereum-lists/chains/blob/master/_data/chains/eip155-14.json