Convert var to let when appropriate.

src/pixie/blends.nim

@@ -609,7 +609,7 @@ when defined(amd64) and not defined(pixieNoSimd):
     sourceEven = mm_srli_epi16(sourceEven, 8)
     sourceOdd = mm_srli_epi16(sourceOdd, 8)
 
-    var
+    let
       blendedEven = mm_add_epi16(sourceEven, backdropEven)
       blendedOdd = mm_add_epi16(sourceOdd, backdropOdd)
 

src/pixie/fonts.nim

@@ -478,7 +478,7 @@ proc textUber(
     for runeIndex in start .. stop:
       let position = arrangement.positions[runeIndex]
 
-      var path = font.typeface.getGlyphPath(arrangement.runes[runeIndex])
+      let path = font.typeface.getGlyphPath(arrangement.runes[runeIndex])
       path.transform(
         translate(position) *
         scale(vec2(font.scale))

src/pixie/images.nim

@@ -368,7 +368,7 @@ proc applyOpacity*(target: Image | Mask, opacity: float32) {.raises: [].} =
       else:
         let index = i
 
-      var values = mm_loadu_si128(target.data[index].addr)
+      let values = mm_loadu_si128(target.data[index].addr)
 
       let eqZero = mm_cmpeq_epi16(values, mm_setzero_si128())
       if mm_movemask_epi8(eqZero) != 0xffff: