test(format): keep the expansion signature off the EOF comment newline

An unterminated block comment at the end of a file swallows the
formatter's mandatory final newline, an artifact the token view already
documents as layout; the preproc signature entry now trims it so the
invariant stays about tokens.  The triggering input joins the corpus.

Assisted-by: GLM 5.3

format/format_test.go

@@ -491,7 +491,11 @@ func stmtSignature(f *ast.File) []string {
 		case *ast.Include:
 			out = append(out, "include "+d.Header.Text)
 		case *ast.Preproc:
-			out = append(out, "preproc "+d.Raw)
+			// An unterminated block comment at the end of the file swallows
+			// the formatter's mandatory final newline, exactly the artifact
+			// the token view documents as layout; trimming it keeps the
+			// signature about tokens, not about that newline.
+			out = append(out, "preproc "+strings.TrimRight(d.Raw, " \t\r\n"))
 		}
 	}
 	for _, s := range f.Orphans {

format/testdata/fuzz/FuzzFormatExpansionRoundTrip/062b12d69fb9426b

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("#/*0")