Add selective reset for text attributes vs background

[Lopinosaurus]

Description:

Currently, Rainbow applies a full reset (\e[0m) after styling text, which clears all formatting including text color, styles (bold/italic), and background color. This makes it challenging to maintain a persistent background color while applying different text styles throughout a section.

Use case:

I'm building a syntax-highlighted diff viewer that displays additions and deletions with colored backgrounds (green/red). Within these colored backgrounds, I need to apply different text colors and styles to keywords, strings, comments, etc.

With the current implementation, each Rainbow-styled text resets the background, creating gaps in the background coloring.

Current behavior:

puts Rainbow('').bg(255, 0, 0)      # Set red background
puts Rainbow('keyword').green.bold   # Outputs: \e[32;1mkeyword\e[0m (resets background!)
puts Rainbow('string').cyan          # Background is gone

Desired Behavior

The ability to selectively reset only text attributes without affecting the background:

puts Rainbow('').bg(255, 0, 0)                    # Set red background
puts Rainbow('keyword').green.bold.reset(:text)   # Reset only text color/style
puts Rainbow('string').cyan.reset(:text)          # Background persists
puts Rainbow('').reset(:background)               # Explicitly reset background when done

Proposed API

Add a reset method with optional scope parameter:

Rainbow(text).color.reset(:text)         # Reset text color and styles only (\e[39;22;23;24m)
Rainbow(text).color.reset(:background)   # Reset background only (\e[49m)
Rainbow(text).color.reset(:all)          # Reset everything (\e[0m) - current behavior
Rainbow(text).color.reset               # Default to :all for backward compatibility

Or alternatively, provide methods to emit only the opening codes without automatic reset:

Rainbow.bg_code(255, 0, 0)  # Returns "\e[48;2;255;0;0m" without closing
Rainbow.reset_code(:text)   # Returns "\e[39;22;23;24m"

Thank you for maintaining this excellent library!