Fix: SubstrateConfigBuilder::set_genesis_hash is a no-op

[RomarQ]

SubstrateConfigBuilder::set_genesis_hash is a no-op: the value is stored on the builder but build() never copies it into SubstrateConfigInner, and impl Config for SubstrateConfig never overrides genesis_hash(), so it falls back to the trait default of None.

Offline workflows that rely on the configured genesis hash fail with ExtrinsicError::GenesisHashNotProvided:

let config = SubstrateConfig::builder()
    .set_genesis_hash(genesis_hash)
    .set_metadata_for_spec_versions(...)
    .set_spec_version_for_block_ranges(...)
    .build();
let client = OfflineClient::<SubstrateConfig>::new_with_config(config);
let at_block = client.at_block(0u64)?;
at_block.tx().create_signable_offline(&call, params)?; // GenesisHashNotProvided

The OnlineClient path is unaffected, since the hash is fetched from the network when genesis_hash is None.

This adds the missing genesis_hash field on SubstrateConfigInner, propagates it through build(), and overrides Config::genesis_hash for SubstrateConfig.