Fix testnet IBC connection lookup and improve fallback robustness

[JohnnyWyles]

The workflow was failing when generating assetlists for testnet (osmo-test-5)

Root causes:

1. IBC lookup didn't distinguish between testnet and mainnet, so testnet assets couldn't find their IBC connections in chain-registry/testnets/_IBC/
2. The fallback mechanism (using path from zone_asset) created the IBC hash but didn't create a trace object, causing downstream crashes in setTransferMethods

Solution

1. Zone-aware IBC lookup

• Added getIBCFilePropertyForZone() that determines which _IBC directory to use based on the zone being processed
• For testnet zones (osmosistestnet): uses chain-registry/testnets/_IBC/
• For mainnet zones (osmosis): uses chain-registry/_IBC/

2. Enhanced fallback mechanism

• When IBC connection isn't found in registry, the existing fallback uses the path from zone_asset
• Now also creates a minimal trace object with all required counterparty information
• Prevents crashes in setTransferMethods when trying to access trace properties

3. Defensive checks

• Added validation in setTransferMethods to only create IBC transfer method if trace has required fields
• Prevents undefined access errors if trace is incomplete