fix: resolve drawImage scaling penalty on non-square sprite height (#3320)

## Description:

This PR resolves a performance parsing penalty in the `UnitLayer`
rendering loop by fixing two issues with non-square sprites:
1. `drawImage` was incorrectly using `sprite.width` for both width and
height, causing aspect ratio squashing and forcing the browser to
perform a scaling operation on the image instead of hitting the canvas
fast-path. It now correctly uses `sprite.height` for the vertical
dimension.
2. `clearUnitsCells` was previously configured to only clear a square
grid (`clearsize`) based solely on width, meaning taller sprites would
leave visual artifact "ghosts" on the map. The clearing bounds have been
corrected to leverage discrete `sprite.width` and `sprite.height`.
Additionally, these values are wrapped in `Math.round()` prior to offset
calculation to prevent subpixel anti-aliasing CPU penalties during
`clearRect`.

## Please complete the following:

- [x] I have added screenshots for all UI updates (not needed)
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file (no new text)
- [x] I have added relevant tests to the test directory (existing tests
suffice, change was minuscule and non-breaking)
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:
skigim

src/client/graphics/layers/UnitLayer.ts

@@ -290,14 +290,15 @@ export class UnitLayer implements Layer {
       .filter((unitView) => isSpriteReady(unitView))
       .forEach((unitView) => {
         const sprite = getColoredSprite(unitView, this.theme);
-        const clearsize = sprite.width + 1;
         const lastX = this.game.x(unitView.lastTile());
         const lastY = this.game.y(unitView.lastTile());
+        const clearX = Math.round(lastX - sprite.width / 2);
+        const clearY = Math.round(lastY - sprite.height / 2);
         this.context.clearRect(
-          lastX - clearsize / 2,
-          lastY - clearsize / 2,
-          clearsize,
-          clearsize,
+          clearX - 1,
+          clearY - 1,
+          sprite.width + 2,
+          sprite.height + 2,
         );
       });
   }
@@ -611,7 +612,7 @@ export class UnitLayer implements Layer {
         Math.round(x - sprite.width / 2),
         Math.round(y - sprite.height / 2),
         sprite.width,
-        sprite.width,
+        sprite.height,
       );
       if (!targetable) {
         this.context.restore();