Simplify reduction operation implementations and error handling

(Targeting feat/compress-keys for now, as it requires significant refactoring to work for trunk right now)

Simplifies the implementation of reduction operation by moving the boilerplate iteration over applicable sources and/or keys to some generic machinery, as well as adding some custom exception types to propagate fatal error conditions from the ReduceWriter initializer back to the CLI and exit gracefully without an unchecked exception.

added 1 commit

• 8d415915 - Move exdf.data_reduction.writer to exdf.data_reduction.red_writer

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added 5 commits

• b823aa91 - 1 commit from branch feat/compress-keys
• 39a96887 - Move exdf.data_reduction.writer to exdf.data_reduction.red_writer
• 1e966a2f - Simplify reduction operation handlers
• b1f57c79 - Add custom exception type to propagate fatal errors from ReduceWriter
• 185a0ae1 - Minor text, comment and code formatting improvements

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added 6 commits

• f1ad47d1 - Merge branch 'feat/compress-keys' into 'master'
• 958316d3 - Move exdf.data_reduction.writer to exdf.data_reduction.red_writer
• 82bb19d5 - Simplify reduction operation handlers
• 26527b5d - Add custom exception type to propagate fatal errors from ReduceWriter
• 919e26f9 - Minor text, comment and code formatting improvements
• d3aecb21 - Add more debug logging when handling reduction operations

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merged

mentioned in commit 85135a0b

mentioned in commit 3f8ba9ba