4.15 sdds::Reader live-file and lifecycle operations

• name:
  Reader::readNewRows, Reader::disconnect, Reader::reconnect, Reader::close
• description:
  Poll an updateable final page without blocking, temporarily release a path-backed file handle, reopen it after identity checks, or close a reader. Live row polling is limited to uncompressed binary files with an updateable final page.
• synopsis:
  std::optional<sdds::PageDelta> readNewRows(  
      sdds::ReadRequest request = {});  
  void disconnect();  
  void reconnect();  
  void close();

• arguments:
  • request — Projection applied to newly observed rows.
• return value:
  readNewRows returns an empty optional when the file has not grown. Otherwise it returns a PageDelta containing the one-based page number, first new zero-based row, and a page containing only new rows.
• exceptions:
  sdds::StateError for an unsupported source, compression, or page mode; sdds::IoError if reopening fails or the file was replaced.
• see also:
  Sections 4.20 and 4.16.