[Feature Request] Last layer feature (latent feature) output in deepmd-kit function or CLI

### Summary In DeePMD-kit we have `eval-desc` CLI based on `eval_descriptor` function to generate structural features from all the DeepPot models for structural distinction. However, for single-model uncentainty quantification, last layer feature is needed for UQ models to map model latent feature to uncentainty quantification. Practical examples are Gaussian Mixture Model [1] and Shallow Ensemble methods [2]. For integrating modern single-model UQs in deepmd-kit, especially DPA LAM, the generation of last layer feature is needed. Ref: [1] Zhu, A.; Batzner, S.; Musaelian, A.; Kozinsky, B. [Fast Uncertainty Estimates in Deep Learning Interatomic Potentials. ](https://doi.org/10.1063/5.0136574) J. Chem. Phys. 2023, 158, 164111. [2] Kellner, M.; Ceriotti, M. Uncertainty Quantification by Direct Propagation of Shallow Ensembles. Mach. Learn.: Sci. Technol. 2024, 5 (3), 035006. https://doi.org/10.1088/2632-2153/ad594a. ### Detailed Description 1. Python functions for calculate last layer feature for all types of deepmd-kit models (especially DPA3) 2. CLI interface like `dp eval-latent` to dump last layer feature like `dp eval-desc` ### Further Information, Files, and Links _No response_