Fix backslash handling in table cell code spans (#1400)

Only strip escaped pipe characters in table cells, preserving other
backslashes for proper markdown processing in code spans.

Fixes #1395

### Before

<img width="40%" alt="Screenshot 2025-08-11 at 14 02 11"
src="https://github.com/user-attachments/assets/8b75766b-bcff-40eb-b29b-d098d949577f"
/>

### After

<img width="40%" alt="Screenshot 2025-08-11 at 14 02 18"
src="https://github.com/user-attachments/assets/dd28681d-41c1-44ce-a03d-d335ac21d7d6"
/>

Author: st0012

lib/rdoc/markdown.kpeg

@@ -1253,7 +1253,7 @@ TableRow = ( ( TableItem:item1 TableItem2*:items { [item1, *items] } ):row | Tab
 	   { row }
 TableItem2 = "|" TableItem
 TableItem = < /(?:\\.|[^|\n])+/ >
-	    { text.strip.gsub(/\\(.)/, '\1')  }
+	    { text.strip.gsub(/\\([|])/, '\1')  }
 
 TableLine = ( ( TableAlign:align1 TableAlign2*:aligns {[align1, *aligns] } ):line | TableAlign2+:line ) "|"? @Newline
 	    { line }

test/rdoc/rdoc_markdown_test.rb

@@ -1157,6 +1157,36 @@ def test_gfm_table_with_links_and_code
     assert_equal expected, doc
   end
 
+  def test_gfm_table_with_backslashes_in_code_spans
+    doc = parse <<~MD
+    Plain text: `$\\\\` and `$\\\\ ` should work.
+
+    | Context | Code | Expected |
+    |---------|------|----------|
+    | Plain   | `$\\\\` | Should show backslash |
+    | Escaped | `$\\\\ ` | Should show backslash |
+    | Multiple| `\\\\n\\\\t` | Should show backslashes |
+    MD
+
+    head = %w[Context Code Expected]
+    align = [nil, nil, nil]
+
+    body = [
+      ['Plain', '<code>$\\\\</code>', 'Should show backslash'],
+      ['Escaped', '<code>$\\\\</code>', 'Should show backslash'],
+      ['Multiple', '<code>\\\\n\\\\t</code>', 'Should show backslashes'],
+    ]
+
+    expected_table = @RM::Table.new(head, align, body)
+
+    expected = doc(
+      para('Plain text: <code>$\\\\</code> and <code>$\\\\</code> should work.'),
+      expected_table
+    )
+
+    assert_equal expected, doc
+  end
+
   def parse(text)
     @parser.parse text
   end