[BUG] Only the first frame is read using abacus/lcao/relax

### Bug summary When reading the abacus relaxation trajectory, dpdata's LabeledSystem only includes the first frame in the trajectory, namely the configuration without any relaxation. @dosu ### dpdata Version v1.0.1 ### Input Files, Running Commands, Error Log, etc. python code as follows, ``` from dpdata import LabeledSystem import os sys = LabeledSystem("./test/chempot=0.02",fmt='abacus/lcao/relax') print(sys) ``` the related directory of abacus results is linked below "Further Information, Files, and Links". The output is ``` Data Summary Labeled System ------------------- Frame Numbers : 1 Atom Numbers : 92 Including Virials : Yes Element List : ------------------- Cu Zn 91 1 ``` but this trajectory should include 11 frames. ### Steps to Reproduce simply unzip the abacus directory and run the python code mentioned above ### Further Information, Files, and Links [test.zip](https://github.com/user-attachments/files/25958453/test.zip)