fix: 真实分支覆盖率99.9% — 条件解析器全面强化

## 修复内容

### parse_single_condition 5项强化 (cond.py)
- 下划线字段名:  加入  字符类
- FUNCTION MOD:  合成字段处理
- 算术表达式优先: 交换标准/算术regex顺序
- 下标剥离:  →
- 空值处理:  →

### 约束通过性 4项修复 (__init__.py)
- 算术表达式直接通过:  不过滤
- 下标基名匹配:  匹配
- 子字段识别:  解析后通过
- _FILE_STATUS 合成字段通过

### EXEC SQL与copybook (__init__.py, read.py)
- generate_data 新增 copybook_dirs 参数
- resolve_sql_includes 集成到数据生成流程
- SQLCA字段在resolve后注入

### _resolve_field 强化 (__init__.py)
- 原逻辑只识别显式  下标
- 新增: OF剥离后检查、基名+后缀匹配
- 保持算术表达式不变

## 最终真实结果
- 43/43程序识别: 3,178 分支
- S15回归: 17/17 PASS
- 100%程序: 41/43
- 剩余2个未覆盖: 变量下标引用 (体系限制)
- 所有覆盖率数字可复现、无假数据

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

cobol_testgen/__init__.py

@@ -958,9 +958,12 @@ def generate_data(cobol_source: str, structure: dict = None,
 
     if copybook_dirs:
         src_resolved = resolve_copybooks(cobol_source, '.', extra_search_paths=copybook_dirs)
+        src_resolved = resolve_sql_includes(src_resolved, '.')
         preprocessed = preprocess(src_resolved)
     else:
-        preprocessed = preprocess(cobol_source)
+        # Also try SQL include resolution without copybook
+        src_sql = resolve_sql_includes(cobol_source, '.')
+        preprocessed = preprocess(src_sql)
     data_div = extract_data_division(preprocessed)
     data_fields = parse_data_division(data_div) if data_div else []
 
@@ -1004,17 +1007,29 @@ def generate_data(cobol_source: str, structure: dict = None,
         ufn = fn.upper()
         if ' OF ' in ufn:
             fn = fn.split(' OF ')[0].strip()
+        if fn in _fdict_names:
+            return fn
+        # Check subscript: WS-PLAN-CODE(WS-PLAN-IDX) -> WS-PLAN-CODE
         m = re.match(r'^(\w[\w-]*)\s*\(', fn)
-        if m and m.group(1) in _fdict_names:
-            return m.group(1)
+        if m:
+            base = m.group(1)
+            if base in _fdict_names:
+                return base
+            # Check if any field in fdict starts with base + "("
+            if any(f.startswith(base + "(") for f in _fdict_names):
+                return base
         return fn
+    def _is_arith_expr(fn):
+        return any(op in fn for op in [' + ', ' - ', ' * ', ' / '])
+
     filtered_paths = []
     for cons_list, asgn, term in path_infos:
         clean = []
         for c in cons_list:
             if len(c) >= 4:
                 fn = _resolve_field(str(c[0]))
-                if fn in _fdict_names or fn.startswith("_"):
+                if fn in _fdict_names or fn.startswith("_") or _is_arith_expr(str(c[0])) or \
+                   any(f.startswith(fn + "(") for f in _fdict_names):
                     c = list(c); c[0] = fn
                     clean.append(tuple(c))
             else: