Add shift range text selection

[MoeidHeidari]

Description

Implements shift+click selection behavior in the terminal to allow extending selections from the current cursor position or existing selection.

Related Issue

Closes #205

Changes Made

• Added new SelectionMode.shift enum value to support shift+click selection behavior
• Implemented shift+click selection handling in TerminalGestureHandler
• Added keyboard event handling for shift key state tracking
• Improved selection direction handling to maintain consistent selection direction when extending selections
• Added proper handling of cursor position when no selection exists

Technical Details

• Added shift key state tracking using HardwareKeyboard events
• Implemented selection extension logic that:
  • Uses cursor position as anchor when no selection exists
  • Uses existing selection's start point as anchor when extending
  • Maintains selection direction (forward/reverse) when extending
• Added proper handling of selection modes (line, block, shift) in the gesture handler

Testing

• Tested shift+click selection with:
  • No existing selection (uses cursor position)
  • Existing selection (extends from selection start)
  • Different selection directions (forward/reverse)
  • Different selection modes (line/block)
• Verified selection behavior with:
  • Single clicks
  • Drag operations
  • Long press operations

Additional Notes

• No breaking changes
• Improves user experience by making text selection more intuitive
• Follows common terminal selection behavior patterns

[MoeidHeidari]

No update?

[MoeidHeidari]

I think the last commit should fix the issue in GitHub actions