Improve error message on type mismatch

Before:

     Key 'group.d' is not an date-local but map[type:date-local value:1979-05-27]:
       Expected:     map[string]interface {}{"type":"date-local", "value":"1979-05-27"}
       Your encoder: map[string]interface {}{"type":"date", "value":"1979-05-27"}

After:

     Key "group.d" is not "date-local" but "date":
       Expected:     map[string]any{"type":"date-local", "value":"1979-05-27"}
       Your encoder: map[string]any{"type":"date", "value":"1979-05-27"}

Author: arp242

json.go

@@ -241,15 +241,15 @@ func isValue(m map[string]any) bool {
 }
 
 func (r Test) mismatch(wantType string, want, have any) Test {
-	return r.fail("Key '%[1]s' is not an %[2]s but %[5]s:\n"+
-		"  Expected:     %#[3]v\n"+
-		"  Your encoder: %#[4]v",
-		r.Key, wantType, want, have, fmtType(have))
+	return r.fail("Key %[1]q is not %[2]q but %[5]q:\n"+
+		"  Expected:     %s\n"+
+		"  Your encoder: %s",
+		r.Key, wantType, fmtHashV(want), fmtHashV(have), fmtType(have))
 }
 
 func (r Test) valMismatch(wantType, haveType string, want, have any) Test {
-	return r.fail("Key '%s' is not an %s but %s:\n"+
-		"  Expected:     %#[3]v\n"+
-		"  Your encoder: %#[4]v",
-		r.Key, wantType, want, have)
+	return r.fail("Key %q is not %q but %q:\n"+
+		"  Expected:     %s\n"+
+		"  Your encoder: %s",
+		r.Key, wantType, haveType, fmtHashV(want), fmtHashV(have))
 }

toml.go

@@ -135,6 +135,5 @@ func isTomlValue(v any) bool {
 }
 
 // fmt %T with "interface {}" replaced with "any", which is far more readable.
-func fmtType(t any) string {
-	return strings.ReplaceAll(fmt.Sprintf("%T", t), "interface {}", "any")
-}
+func fmtType(t any) string  { return strings.ReplaceAll(fmt.Sprintf("%T", t), "interface {}", "any") }
+func fmtHashV(t any) string { return strings.ReplaceAll(fmt.Sprintf("%#v", t), "interface {}", "any") }