fix: correct data format parsing and make start time parameter required

[rubenszinho]

This PR includes several important fixes and improvements to the command-line interface and data processing logic:

Major Changes

• Fixed the column order parsing to match the actual ENEMETER data format (TIME_DELTA, VOLTAGE, CURRENT, TEMP)
• Made the start time parameter (--start) required and enforced time-of-day inclusion
• Added proper handling for type casting in flag parameter parsing
• Fixed voltage calculation to use absolute values for power computation
• Updated documentation and examples throughout the codebase

Specific Improvements

• Added detailed validation and error messages for required parameters
• Added warning when start time appears to be exactly midnight (possibly missing time of day)
• Fixed command name references in help text (enemeter-cli → enemeter-data-processing)
• Updated README.md to reflect new requirements and usage patterns
• Improved error handling in CSV parsing
• Fixed unit conversions to be more consistent

Testing Done

• Successfully processed ESP32 data files with the new column format
• Verified error messages when required parameters are missing
• Tested time filtering with different start time formats

These changes should make the tool more robust and user-friendly while fixing the data parsing issues that were causing incorrect readings.