fix: trendseries serialization + require signal in coverage endpoint
fix: trendseries serialization + require signal in coverage endpoint

cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata