chore(PSDK-640): add network_id to WalletData

[0xRAG]

What changed? Why?

It should be clear which saved wallets belong to which networks when you save_seed / export_data for a given wallet.

How i tested

After running:

# Create a new wallet
wallet = Wallet.create(network_id="base-mainnet")

print(wallet.export_data())

# Save the wallet seed
wallet.save_seed("/Users/ryan/code/public/seeds/wallet_seed.json")

wallet_seed.json looks like:

{
  "11cd62ab-0046-472d-bb16-3ad560bdf2d4": {
        "seed": "21exxx",
        "encrypted": false,
        "auth_tag": "",
        "iv": "",
        "network_id": "base-mainnet"
    }
}

And the result of wallet.export():

WalletData: (wallet_id: 11cd62ab-0046-472d-bb16-3ad560bdf2d4, seed: 21exxx, network_id: base-mainnet)

Qualified Impact

The network id should always be present, and if it is not, it will simply not be included in the WalletData

[John-peterson-coinbase]

Please add new changes under Unreleased heading until the new release is being cut

[John-peterson-coinbase]

Return type can be None -> str | None