DIGIT-2432 Ensure mouse focus scrolls cell into view

[Mrprey]

Description ✍️

This Pull Request improves the UX of PlutoGrid by ensuring that when a user taps a cell, the grid automatically scrolls to bring the selected cell into view — both vertically and horizontally. This eliminates the need for manual scrolling when interacting with off-screen cells.

Key Changes:

• Introduced _ensureCellVisibility() method in PlutoGridCellGestureEvent to centralize scroll logic.
• Ensures both row and column visibility using precise offset calculations based on viewport size and scroll extents.
• Updates gesture handlers (onTapUp, onLongPressStart) to trigger visibility adjustments when a cell is selected or edited.
• Added comprehensive unit tests to verify behavior under various scroll conditions.

Overview 👀

✅ Before

• Tapping a cell outside of the viewport didn’t automatically scroll to it.
• Users had to manually scroll to bring selected cells into view.

✅ After

• Grid now scrolls both vertically and horizontally to reveal the selected cell.
• Behavior works for both selecting and editing states.

Visual Example (not included, optional):

Imagine tapping a cell far to the right — the grid auto-scrolls to bring it into view.

How to Smoke? 👷‍♂️

1. Open a PlutoGrid with multiple rows and columns, enough to require scrolling.
2. Scroll to hide part of the grid (e.g., scroll down and right).
3. Tap a cell that is not currently visible.
4. ✅ Confirm:
   • The grid scrolls to bring the tapped cell into view.
   • The cell enters editing mode (if expected).
5. Run unit tests:

   flutter test test/src/manager/event/pluto_grid_cell_gesture_event_test.dart

6.Pay special attention to:

• should reposition vertical scroll when tapped row is above viewport
• should reposition horizontal scroll when tapped column is clipped

[rodiguif]

LGTM!
The behavior is perfect.