Fix edge key popup: use hitbox bounds in squaredDistanceToEdge

[AZADAYAZ]

Problem

On edge keys (leftmost column: 1, Q, A and rightmost column: 0, Ü, İ), key preview popups do not appear during normal tapping — they only show up when long-pressing. Additionally, when the finger is in the extended hitbox area (near the screen edge), the popup panel cannot correctly detect finger position.

Root Cause

The squaredDistanceToEdge() method in Key.java uses the visual bounds of the key (getX(), mWidth, getY(), mHeight) for distance calculations. However, for edge keys, markAsLeftEdge() and markAsRightEdge() extend the hitbox (mHitBox) beyond the visual bounds. This inconsistency creates the following problem:

1. isOnKey() correctly uses the extended hitbox → the touch is recognized as being on the key
2. 2. squaredDistanceToEdge() uses visual bounds → the distance from the visual edge is very large
3. 3. Result: PointerTracker in isMajorEnoughMoveToBeOnNewKey() interprets the finger as having left the key, canceling the key preview popup
      Since the long-press flow (onLongPressed) does not perform this distance check, long-press popups still work — which is why the issue only manifests during normal tapping.

Fix

Changed squaredDistanceToEdge() to use mHitBox bounds instead of visual bounds:

- final int left = getX();
- - final int right = left + mWidth;
- - final int top = getY();
- - final int bottom = top + mHeight;
- + final int left = mHitBox.left;
- + final int right = mHitBox.right - 1;
- + final int top = mHitBox.top;
- + final int bottom = mHitBox.bottom - 1;
- ```
## Impact Analysis

| Usage | File | Effect |
|-------|------|--------|
| Nearest key selection | `KeyDetector.java` | No change — already filtered by `isOnKey()` hitbox check |
| Finger-off-key detection | `PointerTracker.java` | **Primary fix** — edge keys now correctly recognized |
| Popup key selection | `PopupKeysDetector.java` | **Positive effect** — extended hitbox now used for proximity |

## Backward Compatibility

For interior keys, `mHitBox` equals the visual bounds, so existing behavior is fully preserved. The fix only affects edge keys where the hitbox has been explicitly extended.