feat(gno): support simulated and dynamic gas pricing for tx fees

[aronpark1007]

Summary

• Adds two new gas-pricing modes for the gno transaction plugin alongside the existing fixed fee: simulate (dry-run the tx via .app/simulate to get the actual gas used, then price it with the fixed linear formula) and dynamic (query gno's own protocol-level auth/gasprice, an EIP-1559-style base fee recomputed per block from actual usage).
• Config.gas_config selects the mode (fixed / simulate / dynamic); the legacy fee field is still accepted for backward compatibility (deprecated, mapped to fixed).
• Denom resolution is fail-fast: if the chain reports no gas-price denom and no denom override is configured, fee construction now errors instead of silently producing a denom-less coin string.

Test plan

• cargo test -p gno-client: parser/pricing/denom-fallback unit tests, including regression coverage for pricing off the post-multiplier gas limit.
• cargo test -p voyager-transaction-plugin-gno: config deserialization (new gas_config schema, legacy fee fallback, both-set precedence, missing-both error).
• Verified on union-devnet after migrating the gno light client contract — confirmed working on-chain.

[aronpark1007]

TODO once #5478 lands: add a BroadcastTxCommitError::SimulationFailed arm in the gno tx plugin so it goes through the same permanent-failure handling as TxFailed. Right now a simulation failure from simulate/dynamic_gas_price would just retry forever.