feat(encode): write the TOML 1.1 output form

Assisted-by: DeepSeek V4.1 Flash

cmd/interpres-decode/main_test.go

@@ -307,13 +307,13 @@ func TestRunEncoderScalars(t *testing.T) {
 		t.Fatalf("Run returned %d, stderr = %q", code, stderr.String())
 	}
 	want := "b = false\n" +
-		"dt = 1979-05-27T07:32:00-07:00\n" +
+		"dt = 1979-05-27T07:32-07:00\n" +
 		"f = inf\n" +
 		"g = 1.5\n" +
 		"i = -9223372036854775808\n" +
 		"ld = 1979-05-27\n" +
-		"ldt = 1979-05-27T07:32:00\n" +
-		"lt = 07:32:00.999000000\n" +
+		"ldt = 1979-05-27T07:32\n" +
+		"lt = 07:32:00.999\n" +
 		"nl = \"line1\\nline2\"\n" +
 		"s = \"quote \\\" and backslash \\\\\"\n"
 	if stdout.String() != want {