add a public API to register data types dynamically

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e239d0b) 82.95% compared to head (bed865f) 82.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #532 +/- ## ======================================= Coverage 82.95% 82.96% ======================================= Files 73 73 Lines 6494 6497 +3 ======================================= + Hits 5387 5390 +3 Misses 1107 1107 ``` | [Files Changed](https://app.codecov.io/gh/deepmodeling/dpdata/pull/532?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/532?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling#diff-ZHBkYXRhL3N5c3RlbS5weQ==) | `85.65% <100.00%> (+0.06%)` | :arrow_up: |

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