feat: improved network selection in typescript/create-onchain-agent

[CarsonRoscoe]

Description

The old selection put ALL networks (EVM & SVM, mainnets & testnets, even custom chain id) into one big select list.
This PR organizes this select into multiple smaller selections.

2. This fixes the "Custom Chain ID". Previously, a chain_id could be assigned, but no custom rpc was gathered, and you could still choose Privy (which does not expose a convenient way to customize by chainId/rpcUrl).

Now, going into the "Custom Chain ID" takes you through a different route entirely. You have to provide an accompanying rpc url, and a new api route is copied. This new API route is custom-evm/viem, which mirrors evm/viem, except rather than assigning a preconfigured Viem chain, it creates a new chain and assigns the chainId/rpc.

This new route already has the fixes from #468 and #484 built into it, so no fast follow will be required to bring it to parity after the merges.

Tests

Tested via manual trial and error down each CLI path and generated the results

[cb-heimdall]

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