fn apply_source_envelope_encoding(
scx: &StatementContext<'_>,
envelope: &SourceEnvelope,
format: &Option<FormatSpecifier<Aug>>,
key_desc: Option<RelationDesc>,
value_desc: RelationDesc,
ignore_keys: Option<bool>,
include_metadata: &[SourceIncludeMetadata],
metadata_columns_desc: Vec<(&str, ColumnType)>,
source_connection: &GenericSourceConnection<ReferencedConnection>,
) -> Result<(RelationDesc, SourceEnvelope, Option<SourceDataEncoding<ReferencedConnection>>), PlanError>