fix(stageb): ParserStmtBox skip_ws静的呼び出し化 - Phase 25.1

**変更内容**:
- ctx.skip_ws(src, j) → ParserStringUtilsBox.skip_ws(src, j) (20箇所)
  - ParserStmtBox.parse: 13箇所
  - ParserStmtBox.parse_using: 7箇所

**理由**:
- MIRレベルでctx（ParserBox instance）がString化する問題を根本回避
- 箱理論的に正しい設計: scan utility = static box統一
- Region+next_iパターンと一貫性維持（LoopForm v2設計準拠）

**影響範囲**:
- lang/src/compiler/parser/stmt/parser_stmt_box.hako のみ
- using追加: ParserStringUtilsBox

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

lang/src/compiler/parser/stmt/parser_stmt_box.hako

@@ -6,6 +6,7 @@
 using sh_core as StringHelpers  // Required: using chain resolution not implemented
 using lang.compiler.parser.stmt.parser_control_box
 using lang.compiler.parser.stmt.parser_exception_box
+using lang.compiler.parser.scan.parser_string_utils_box as ParserStringUtilsBox
 
 static box ParserStmtBox {
   parse(src, i, ctx) {
@@ -21,7 +22,7 @@ static box ParserStmtBox {
         env.set("HAKO_STAGEB_STMT_DEPTH", "1")
       }
     }
-    local j = ctx.skip_ws(src, i)
+    local j = ParserStringUtilsBox.skip_ws(src, i)
     // VM 差分で skip_ws が前進しないパスがあったため、手動で最小限の空白スキップをフォローする。
     {
       local n = src.length()
@@ -50,19 +51,19 @@ static box ParserStmtBox {
           print("[parser/stmt] kind=extern_c j=" + ("" + j))
         }
       }
-      j = j + 9 // len("@extern_c")
+      j = j + 9 // len(\"@extern_c\")
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       if j < src.length() && src.substring(j, j+1) == "(" { j = j + 1 }
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       // First string literal: symbol
       local sym = ""
       if j < src.length() && src.substring(j, j+1) == "\"" {
         sym = ctx.read_string_lit(src, j)
         j = ctx.gpos_get()
       }
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       if j < src.length() && src.substring(j, j+1) == "," { j = j + 1 }
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       // Second string literal: func
       local func_name = ""
       if j < src.length() && src.substring(j, j+1) == "\"" {
@@ -70,10 +71,10 @@ static box ParserStmtBox {
         j = ctx.gpos_get()
       }
       // Skip to ')' if present
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       if j < src.length() && src.substring(j, j+1) == ")" { j = j + 1 }
       // Optional semicolon is consumed by caller; still advance if present
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       if j < src.length() && src.substring(j, j+1) == ";" { j = j + 1 }
       ctx.gpos_set(j)
       // Record annotation in parser context and emit no statement
@@ -106,7 +107,7 @@ static box ParserStmtBox {
         }
       }
       j = j + 6
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       local default_ret = "{\"type\":\"Int\",\"value\":0}"
       local expr_json_ret = default_ret
       local end_pos_ret = j
@@ -149,14 +150,14 @@ static box ParserStmtBox {
         }
       }
       j = j + kw_len
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       local idp = ctx.read_ident2(src, j)
       local at = idp.lastIndexOf("@")
       local name = idp.substring(0, at)
       j = ctx.to_int(idp.substring(at+1, idp.length()))
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       if j < src.length() && src.substring(j, j+1) == "=" { j = j + 1 }
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       local default_local = "{\"type\":\"Int\",\"value\":0}"
       local expr_json_local = default_local
       local end_pos_local = j
@@ -269,13 +270,13 @@ static box ParserStmtBox {
       if at0 > 0 {
         local name0 = idp0.substring(0, at0)
         local k0 = ctx.to_int(idp0.substring(at0+1, idp0.length()))
-        k0 = ctx.skip_ws(src, k0)
+        k0 = ParserStringUtilsBox.skip_ws(src, k0)
         if k0 < src.length() && src.substring(k0, k0+1) == "=" {
           local eq_two = "="
           if k0 + 1 < src.length() { eq_two = src.substring(k0, k0+2) }
           if eq_two != "==" {
             k0 = k0 + 1
-            k0 = ctx.skip_ws(src, k0)
+            k0 = ParserStringUtilsBox.skip_ws(src, k0)
             local default_local = "{\"type\":\"Int\",\"value\":0}"
             local expr_json0 = default_local
             local end_pos0 = k0
@@ -321,16 +322,16 @@ static box ParserStmtBox {
   // Parse using statement
   parse_using(src, i, stmt_start, ctx) {
     local j = i + 5  // skip "using"
-    j = ctx.skip_ws(src, j)
+    j = ParserStringUtilsBox.skip_ws(src, j)
 
     if src.substring(j, j+1) == "\"" {
       local p = ctx.read_string_lit(src, j)
       j = ctx.gpos_get()
-      j = ctx.skip_ws(src, j)
+      j = ParserStringUtilsBox.skip_ws(src, j)
       local alias = null
       if ctx.starts_with_kw(src, j, "as") == 1 {
         j = j + 2
-        j = ctx.skip_ws(src, j)
+        j = ParserStringUtilsBox.skip_ws(src, j)
         local idp = ctx.read_ident2(src, j)
         local at = idp.lastIndexOf("@")
         alias = idp.substring(0, at)
@@ -345,10 +346,10 @@ static box ParserStmtBox {
         j = ctx.to_int(idp.substring(at+1, idp.length()))
         local cont = 1
         loop(cont == 1) {
-          j = ctx.skip_ws(src, j)
+          j = ParserStringUtilsBox.skip_ws(src, j)
           if src.substring(j, j+1) == "." {
             j = j + 1
-            j = ctx.skip_ws(src, j)
+            j = ParserStringUtilsBox.skip_ws(src, j)
             idp = ctx.read_ident2(src, j)
             at = idp.lastIndexOf("@")
             name = name + "." + idp.substring(0, at)
@@ -357,11 +358,11 @@ static box ParserStmtBox {
             cont = 0
           }
         }
-        j = ctx.skip_ws(src, j)
+        j = ParserStringUtilsBox.skip_ws(src, j)
         local alias2 = null
         if ctx.starts_with_kw(src, j, "as") == 1 {
           j = j + 2
-          j = ctx.skip_ws(src, j)
+          j = ParserStringUtilsBox.skip_ws(src, j)
           idp = ctx.read_ident2(src, j)
           at = idp.lastIndexOf("@")
           alias2 = idp.substring(0, at)