Major stats upgrade.

StatLiteral: just emit a stat in the obvious way. Plus helper functions.

Can also identify stats via struct tags, no more Stored type!

Can also identify stat methods via name (with compatible types).

smoketest/collection.go

@@ -11,6 +11,10 @@ type SmokeTestCollection struct {
 	Turns  cardsim.Invisible[int]
 
 	Flavor cardsim.Stored[string]
+
+	Things       int     `cardsim:"stat"`
+	MoreThings   int     `cardsim:"hidden"`
+	FloatyThings float64 `cardsim:"round1"`
 }
 
 func (c *SmokeTestCollection) Average() float64 {
@@ -23,3 +27,7 @@ func (c *SmokeTestCollection) Stats() []cardsim.Stat {
 	cardsim.SortStats(stats)
 	return stats
 }
+
+func (c *SmokeTestCollection) StatTotalThings() float64 {
+	return float64(c.Things+c.MoreThings) + c.FloatyThings
+}