Make diff_files/diff_files_sorted error on mismatch

Previously these functions returned 1 on mismatch but no caller
checked the return value, allowing roundtrip failures to go
undetected. Now they call error() so the sta process exits
non-zero and the regression runner catches the failure.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Jaehyun Kim <jhkim@precisioninno.com>

Author: jhkim-pii

test/helpers.tcl

@@ -56,14 +56,10 @@ proc diff_files_sorted { file1 file2 } {
   } else {
     for {set i 0} {$i < [llength $lines1] && $i < [llength $lines2]} {incr i} {
       if { [lindex $lines1 $i] ne [lindex $lines2 $i] } {
-        puts "Differences found (sorted)."
-        puts "[lindex $lines1 $i]"
-        puts "[lindex $lines2 $i]"
-        return 1
+        error "diff_files_sorted: $file1 vs $file2 differ at sorted line $i\n< [lindex $lines1 $i]\n> [lindex $lines2 $i]"
       }
     }
-    puts "Differences found (sorted): file lengths differ."
-    return 1
+    error "diff_files_sorted: $file1 vs $file2 differ: file lengths differ"
   }
 }
 
@@ -106,10 +102,7 @@ proc diff_files { file1 file2 { ignore "" } } {
   close $stream1
   close $stream2
   if { $found_diff || $line1_length != $line2_length } {
-    puts "Differences found at line $line."
-    puts "$line1"
-    puts "$line2"
-    return 1
+    error "diff_files: $file1 vs $file2 differ at line $line\n< $line1\n> $line2"
   } else {
     puts "No differences found."
     return 0