fn merge_funding_streams(
funding_streams: Option<Vec<ConfiguredFundingStreams>>,
pre_nu6_funding_streams: Option<ConfiguredFundingStreams>,
post_nu6_funding_streams: Option<ConfiguredFundingStreams>,
) -> Result<Option<Vec<ConfiguredFundingStreams>>, &'static str>Expand description
Merge legacy streams before the current list, preserving omission and explicit disable.