Intcode Reset optimization

Initially I noticed that I was copying twice unnecessarily (once in init() after nulling out memory, and again after returning from init()). After cleaning that up, I realized that we don't need to create a new buffer at all if the program never malloc-ed, so sometimes we can skip the re-init and we can always avoid the double-copy. I don't know if this is actually measurable anywhere, but I spot-checked some results and I still seem to be getting the same answers, so I'm gonna roll with it.

utilities/intcode.go

@@ -127,9 +127,15 @@ func (p *IntcodeProgram) ensureMemoryCapacity(address int) {
 }
 
 func (p *IntcodeProgram) Reset() {
-	p.memory = nil
+	wiped := false
+	if len(p.memory) != len(p.program) {
+		wiped = true
+		p.memory = nil
+	}
 	p.init()
-	copy(p.memory, p.program)
+	if !wiped {
+		copy(p.memory, p.program)
+	}
 	p.relativeBase = 0
 }