chore: chain refactoring

[onyb]

This refactoring has two goals:

1. Introduce chain IDs for non-EVM and Solana chains, such as Bitcoin, ZCash, Filecoin, etc. This follows the convention we follow in brave-core.
2. Centralise all chain-specific information, such as Simplehash ID, Alchemy ID, etc., within the same enum. This avoids the need to maintain mappings like ChainIdCoinTypeMap, AlchemyChain, SimpleHashChain, etc.

Consequently, the ChainId enum has been removed.

This PR also fixes a unit test which was making real calls to the Coingecko API.