feat: 新增 BooleanFunctionLookup 支持函数式操作符

- sqlgen: 新增 BooleanFunctionLookup，生成 FUNC(LHS, RHS) 格式，优先级高于 BooleanOperatorLookup
- dialect/duckdb: 使用 regexp_matches 替代 ~ 实现部分匹配，等价于 MySQL REGEXP
- sqlgen/expression_sql_generator_test: 补充 BooleanFunctionLookup 测试用例，修正 encode_error 前缀
- sqlgen/sql_dialect_options_test: 验证 BooleanFunctionLookup 默认为 nil
- dialect/duckdb_test: 新增 regexp_matches SQL 生成测试

dialect/duckdb/duckdb_test.go

@@ -107,6 +107,32 @@ func TestJoinSQL(t *testing.T) {
 	assert.Contains(t, sql, `ON ("users"."id" = "orders"."user_id")`)
 }
 
+func TestRegexpSQL(t *testing.T) {
+	db := dbv2.Dialect("duckdb")
+
+	// RegexpLike → regexp_matches(col, pattern)
+	ds := db.From("docs").Where(dbv2.C("content").RegexpLike("简介"))
+	sql, _, err := ds.ToSQL()
+	assert.NoError(t, err)
+	assert.Equal(t, `SELECT * FROM "docs" WHERE regexp_matches("content", '简介')`, sql)
+
+	// RegexpILike → 同样生成 regexp_matches
+	ds = db.From("docs").Where(dbv2.C("content").RegexpILike("简介"))
+	sql, _, err = ds.ToSQL()
+	assert.NoError(t, err)
+	assert.Equal(t, `SELECT * FROM "docs" WHERE regexp_matches("content", '简介')`, sql)
+}
+
+func TestRegexpPreparedSQL(t *testing.T) {
+	db := dbv2.Dialect("duckdb")
+
+	ds := db.From("docs").Prepared(true).Where(dbv2.C("content").RegexpLike("简介"))
+	sql, args, err := ds.ToSQL()
+	assert.NoError(t, err)
+	assert.Equal(t, `SELECT * FROM "docs" WHERE regexp_matches("content", $1)`, sql)
+	assert.Equal(t, []interface{}{"简介"}, args)
+}
+
 func TestWindowFunction(t *testing.T) {
 	db := dbv2.Dialect("duckdb")