feat(cosmwasm): introduce escrow vault for fungibility layer (#4937)

A CosmWasm contract that acts as a solver in the zkgm protocol, enabling
fungible token transfers across IBC channels by managing escrowed
assets.

  Key Features

- Dual Token Support: Handles both native Cosmos tokens (via BankMsg)
and CW20 tokens
- Fungible Lane Configuration: Maps (channel_id, base_token) pairs to
counterparty beneficiaries for cross-chain settlement
- Intent Whitelisting: Controls which packet hashes can be filled before
finality
- Solver Interface: Implements DoSolve to release escrowed tokens and
return beneficiary addresses for acknowledgments

  How It Works

1. Admin configures fungible lanes linking channels/tokens to
counterparty beneficiaries
2. When zkgm calls DoSolve, the contract validates the order and
releases escrowed tokens
  3. Relayers receive fees (base_amount - quote_amount)
4. Returns the counterparty beneficiary address for source chain
repayment (symmetric vault)

  Security

- Access controlled: Only zkgm can call DoSolve, only admin can
configure lanes
  - Validates base_amount ≥ quote_amount to prevent underflows
- Intent packets must be whitelisted to prevent unauthorized
pre-finality fills