Add "only" option to accumulate time into single units

[Copilot]

This PR introduces a new only option that allows users to accumulate all time differences into a single specified unit, rather than using the default mixed-unit format.

New Functionality

The only option accepts four values: :years, :months, :weeks, and :days. When specified, it converts the entire time difference into that single unit:

# Before (default behavior)
timeago(Date.today.prev_day(365))
=> "1 year ago"

timeago(Date.today.prev_day(500))
=> "1 year and 4 months ago"

# After (with only option)
timeago(Date.today.prev_day(365), only: :weeks)
=> "52 weeks ago"

timeago(Date.today.prev_day(500), only: :weeks)
=> "71 weeks ago"

timeago(Date.today.prev_day(365), only: :months)
=> "12 months ago"

Integration with Existing Features

The only option works seamlessly with all existing functionality:

# With different styles
timeago(date, only: :weeks, style: :short)
=> "52w ago"

timeago(date, only: :months, style: :array)
=> ["12 months"]

# With localization
timeago(date, only: :weeks, locale: :es)
=> "hace 52 semanas"

# Command line interface (updated to use OptionParser)
timeago 2023-1-1 2024-1-1 --only weeks
=> "52 weeks ago"

Implementation Details

• Added validation for the only option in the core timeago method
• Implemented time unit conversion logic with proper rounding
• Special handling for edge cases (today always returns "today" regardless of only option)
• Small time periods are rounded up to minimum 1 of the specified unit
• Updated CLI to use Ruby's OptionParser for improved argument handling
• Full backward compatibility - all existing behavior is preserved

Testing

• Added 8 comprehensive test cases covering all units and edge cases
• All existing 21 tests continue to pass
• CLI tests validate the new OptionParser integration
• Total test suite: 29 tests, all passing

Documentation

• Updated README with detailed examples and usage instructions
• Added CLI documentation showing the new --only/-o flag with OptionParser
• Included examples combining only with other options

This change addresses the need for users who want consistent time units in their output, particularly useful for data visualization, APIs, or when specific unit granularity is required.

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[markets]

@copilot update from master please, the main change is that in master the CLI now uses OptParser, so update that part.

[Copilot]

@copilot update from master please, the main change is that in master the CLI now uses OptParser, so update that part.

Updated the CLI to use OptionParser structure from master branch. The --only/-o option now integrates cleanly with the new implementation while maintaining all existing functionality. Commit: 3d6c616