feat: add benchmark-programs — 58 telecom COBOL test programs

作为子目录纳入系统，与核心测试管道协同

Co-Authored-By: Claude <noreply@anthropic.com>

benchmark-programs/cross-cutting/variable-length/README.md

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+# Variable-Length Records and Tables
+
+## Test Cases
+
+| Test ID | Description |
+|---------|-------------|
+| VL-N001 | Write varying-length records (14, 34, 84 bytes) |
+| VL-N002 | Read back varying-length records, verify length |
+| VL-N003 | OCCURS DEPENDING ON table with 5 entries |
+| VL-N004 | ODO table resized to 10 entries; zero-length ODO |
+| VL-N005 | Write maximum length record (99 bytes) |
+| VL-N006 | Write minimum length record (1 byte) |
+
+## Features Covered
+- `RECORD IS VARYING IN SIZE FROM 1 TO 99 DEPENDING ON`
+- `OCCURS DEPENDING ON` (ODO) table with dynamic resizing
+- FILE STATUS checking on varying-length operations
+- Sequential fixed-length file with varying logical records
+
+## Expected Results
+All 6 tests should display PASS. Record lengths should match write sizes.