Use clear rather than manual zeroing for Bitmap.Reset.

PiperOrigin-RevId: 650449794

pkg/bitmap/bitmap.go

@@ -253,9 +253,7 @@ func (b *Bitmap) FlipRange(begin, end uint32) {
 // Reset zeroes the entire bitmap.
 func (b *Bitmap) Reset() {
 	b.numOnes = 0
-	for i := range b.bitBlock {
-		b.bitBlock[i] = 0
-	}
+	clear(b.bitBlock)
 }
 
 // ForEach calls `f` for each set bit in the range [start, end).