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

sqlgen/expression_sql_generator.go

@@ -386,10 +386,22 @@ func (esg *expressionSQLGenerator) aliasedExpressionSQL(b sb.SQLBuilder, aliased
 
 // Generates SQL for a BooleanExpresion (e.g. I("a").Eq(2) -> "a" = 2)
 func (esg *expressionSQLGenerator) booleanExpressionSQL(b sb.SQLBuilder, operator exp.BooleanExpression) {
+	operatorOp := operator.Op()
+
+	// 函数式操作符：生成 FUNC(LHS, RHS)
+	if fn, ok := esg.dialectOptions.BooleanFunctionLookup[operatorOp]; ok {
+		b.Write(fn)
+		b.WriteRunes(esg.dialectOptions.LeftParenRune)
+		esg.Generate(b, operator.LHS())
+		b.WriteRunes(esg.dialectOptions.CommaRune, esg.dialectOptions.SpaceRune)
+		esg.Generate(b, operator.RHS())
+		b.WriteRunes(esg.dialectOptions.RightParenRune)
+		return
+	}
+
 	b.WriteRunes(esg.dialectOptions.LeftParenRune)
 	esg.Generate(b, operator.LHS())
 	b.WriteRunes(esg.dialectOptions.SpaceRune)
-	operatorOp := operator.Op()
 	if val, ok := esg.dialectOptions.BooleanOperatorLookup[operatorOp]; ok {
 		b.Write(val)
 	} else {