Description

This PR implements goto_next() and goto_previous() navigation functions as requested in #20. These functions allow programmatic navigation between marks without relying on the UI picker or static keybindings. They use the closest mark within the current file as the current reference position and apply wrap-around navigation when reaching the start/end of the list. This enables plugin authors and advanced users to build custom navigation workflows and integrate marksman’s mark navigation into other tools.

Type of Change

• New feature (non-breaking change which adds functionality)

Testing

• Tests pass locally (just test)
• Added new tests for this change
• Tested manually in multiple scenarios

Describe specific testing done:

• Added goto_next and goto_previous tests including wrap-around
• Verified navigation works when cursor is on a mark, near a mark, and in files with multiple marks
• Verified correct fallback behavior when no marks are in the current file
• Confirmed sensible error behavior when fewer than two marks exist

Breaking Changes

None. This is a new API surface and does not affect existing commands or keymaps.

Checklist

• Code follows style guidelines (just lint passes)
• Code is formatted (just format applied)
• Self-review completed
• Documentation updated (added brief usage notes where appropriate)
• No console logs or debug code left behind

Additional Notes

Resolves #20