feat: 完善扫描器、exec 及 schema 相关功能

- exec/scanner: 用 *interface{} 替换 **json.RawMessage 扫描目标，兼容 DuckDB 返回 map[string]interface{} 的场景；新增 toJSONRawMessage 转换函数
- exec/scanner: ScanVal 支持结构体指针，通过 JSON 中间层转换（DuckDB STRUCT 列）
- exec/scanner: 将 *sql.RawBytes 和 *[]byte 的处理从 ScanValContext 移入 scanner.ScanVal
- exec/query_executor: 简化 ScanValContext，移除私有 scan 方法
- exec: 补充 scanner 级别 ScanVal 测试用例
- internal/util/reflect: 重写 SafeSetVarValue，修复非指针 src 及 nil 指针字段的 panic
- internal/util/column_map: 恢复非匿名带标签结构体字段的展开逻辑
- schema: 新增 vector 列类型支持
- engine: 补充 DuckDB 相关配置
- dialect/sqlite3/vtab: 完善虚拟表适配器
- 各方言测试改用 sqlmock 虚拟连接

go.sum

@@ -18,6 +18,8 @@ github.com/apache/arrow-go/v18 v18.1.0 h1:agLwJUiVuwXZdwPYVrlITfx7bndULJ/dggbnLF
 github.com/apache/arrow-go/v18 v18.1.0/go.mod h1:tigU/sIgKNXaesf5d7Y95jBBKS5KsxTqYBKXFsvKzo0=
 github.com/apache/thrift v0.21.0 h1:tdPmh/ptjE1IJnhbhrcl2++TauVjy242rkV/UzJChnE=
 github.com/apache/thrift v0.21.0/go.mod h1:W1H8aR/QRtYNvrPeFXBtobyRkd0/YVhTc6i07XIAgDw=
+github.com/asg017/sqlite-vec-go-bindings v0.1.6 h1:Nx0jAzyS38XpkKznJ9xQjFXz2X9tI7KqjwVxV8RNoww=
+github.com/asg017/sqlite-vec-go-bindings v0.1.6/go.mod h1:A8+cTt/nKFsYCQF6OgzSNpKZrzNo5gQsXBTfsXHXY0Q=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-sql-driver/mysql v1.7.1 h1:lUIinVbN1DY0xBg0eMOzmmtGoHwWBbvnWubQUrtU8EI=
@@ -58,6 +60,8 @@ github.com/marcboeker/go-duckdb v1.8.5 h1:tkYp+TANippy0DaIOP5OEfBEwbUINqiFqgwMQ4
 github.com/marcboeker/go-duckdb v1.8.5/go.mod h1:6mK7+WQE4P4u5AFLvVBmhFxY5fvhymFptghgJX6B+/8=
 github.com/mattn/go-sqlite3 v1.14.17 h1:mCRHCLDUBXgpKAqIKsaAaAsrAlbkeomtRFKXh2L6YIM=
 github.com/mattn/go-sqlite3 v1.14.17/go.mod h1:2eHXhiwb8IkHr+BDWZGa96P6+rkvnG63S2DGjv9HUNg=
+github.com/mattn/go-sqlite3 v1.14.42 h1:MigqEP4ZmHw3aIdIT7T+9TLa90Z6smwcthx+Azv4Cgo=
+github.com/mattn/go-sqlite3 v1.14.42/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=
 github.com/microsoft/go-mssqldb v1.9.4 h1:sHrj3GcdgkxytZ09aZ3+ys72pMeyEXJowT44j74pNgs=
 github.com/microsoft/go-mssqldb v1.9.4/go.mod h1:GBbW9ASTiDC+mpgWDGKdm3FnFLTUsLYN3iFL90lQ+PA=
 github.com/minio/asm2plan9s v0.0.0-20200509001527-cdd76441f9d8 h1:AMFGa4R4MiIpspGNG7Z948v4n35fFGB3RR3G/ry4FWs=