fix: inferStatePrefix... should default to s1 as the first interm…

…ediate state.

This means setting `currentStateNumber := 0`

Tactics/SymContext.lean

@@ -247,7 +247,7 @@ Falling back to the default numbering scheme, \
 with `s1` as the first new intermediate state"
     modifyThe SymContext ({ · with
       state_prefix := "s",
-      currentStateNumber := 1 })
+      currentStateNumber := 0 })
 
 /-- Annotate any errors thrown by `k` with a local variable (and its type) -/
 private def withErrorContext (name : Name) (type? : Option Expr) (k : MetaM α) :