Module merge

Merge reader implementation.

Structs

• CompareFirst 🔒
  Type to compare Batch by first row.
• MergeReader
  Reader to merge sorted batches.
• MergeReaderBuilder
  Builder to build and initialize a MergeReader.
• Metrics 🔒
  Metrics for the merge reader.
• Node 🔒
  A Node represent an individual input data source to be merged.