limit the filename length dumped by MultiSystems

[njzjz]

Fix #553.

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (5e8f0ba) 82.86% compared to head (0b6f4ee) 82.90%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #554 +/- ## ========================================== + Coverage 82.86% 82.90% +0.04% ========================================== Files 73 73 Lines 6523 6541 +18 ========================================== + Hits 5405 5423 +18 Misses 1118 1118 ``` | [Files](https://app.codecov.io/gh/deepmodeling/dpdata/pull/554?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling) | Coverage Δ | | |---|---|---| | [dpdata/system.py](https://app.codecov.io/gh/deepmodeling/dpdata/pull/554?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling#diff-ZHBkYXRhL3N5c3RlbS5weQ==) | `86.11% <100.00%> (+0.31%)` | :arrow_up: | | [dpdata/utils.py](https://app.codecov.io/gh/deepmodeling/dpdata/pull/554?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling#diff-ZHBkYXRhL3V0aWxzLnB5) | `100.00% <100.00%> (ø)` | |

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