Elevate lerp to 64 bits

For long lines, the linear interpolation for the current position could
overflow. This is the reason the length resolution is currently so
small, which sets a limit on the minimum pen speed. This change
introduces two 64-bit divisions, but allows for a larger length
resolution and lower pen speeds. The runtime is still pretty minimal.

stm32f103t8u6/build_number.txt

@@ -1 +1 @@
-333
+337

stm32f103t8u6/src/pwm_output.c

@@ -197,11 +197,15 @@ void Output_Tick(void)
             Output_CurrentLinePosition += step_length;
             unsigned int remaining = Output_CurrentLineLength
                 - Output_CurrentLinePosition;
-            position.x = (Output_CurrentLineEnd.x * Output_CurrentLinePosition
-                    + Output_CurrentLineStart.x * remaining)
+            position.x = ((long long)Output_CurrentLineEnd.x
+                        * Output_CurrentLinePosition
+                    + (long long)Output_CurrentLineStart.x
+                        * remaining)
                 / Output_CurrentLineLength;
-            position.y = (Output_CurrentLineEnd.y * Output_CurrentLinePosition
-                    + Output_CurrentLineStart.y * remaining)
+            position.y = ((long long)Output_CurrentLineEnd.y
+                        * Output_CurrentLinePosition
+                    + (long long)Output_CurrentLineStart.y
+                        * remaining)
                 / Output_CurrentLineLength;
             break;
         }