Integer type policy

Integers are for numbers, enabling arithmetic like subtractions and for
loops without getting shot in the foot. Unsigneds are for bitfields.

- "int" for numbers that will always be laughably smaller than four
  billion, and where we don't care about the serialization format.

- "int32" for numbers that will always be laughably smaller than four
  billion, and will be serialized to four bytes.

- "int64" for numbers that may approach four billion or will be
  serialized to eight bytes.

- "uint32" and "uint64" for bitfields, depending on required number of
  bits and serialization format. Likewise "uint8" and "uint16", although
  rare in this project since they don't exist in XDR.

- "int8", "int16" and plain "uint" are almost never useful.

internal/lamport/clock_test.go

@@ -17,12 +17,12 @@ package lamport
 
 import "testing"
 
-var inputs = []uint64{0, 42, 2, 3, 4, 8, 9, 33, 44, 112, 100}
+var inputs = []int64{0, 42, 2, 3, 4, 8, 9, 33, 44, 112, 100}
 
 func TestClock(t *testing.T) {
 	c := Clock{}
 
-	var prev uint64
+	var prev int64
 	for _, input := range inputs {
 		cur := c.Tick(input)
 		if cur <= prev || cur <= input {