Use CAIP-2 in Bidyrectional

[volovyks]

• Use Chain in SignBidirectionalEvent in a backwards compatible way (very important) @ChaoticTempest

#[derive(Debug, Clone, Copy)]
pub enum Chain {
    Near,
    Ethereum,
    Solana,
    Bitcoin,
    Hydration,
}

impl Chain {
    pub fn caip2_chain_id(&self) -> &str {
        match self {
            Chain::Near => "near:mainnet",
            Chain::Ethereum => "eip155:1",
            Chain::Solana => "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
            Chain::Bitcoin => "bip122:000000000019d6689c085ae165831e93",
            Chain::Hydration => "polkadot:2034",
        }
    }
}

• Remove usage of dest(), make docs clear @ppca
• Check SignNetJS @esaminu
• Use in Hydration integration @esaminu, do not set dest to avoid confusion

[ChaoticTempest]

honestly, I would prefer to keep dest as it is intuitive what exactly it is. It signifies the destination chain for this transaction. caip2_id on the other hand gives no meaning besides that it is an identifier but for what exactly? source chain? target chain?

[volovyks]

It was decided not to use the dest field and stick to caip2_id as the destination, since that is what it was intended to be used for in Bidirectional flow.