Validate unit on Timeseries flush

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (6023962) 95.71% compared to head (2b82fec) 95.71%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #200 +/- ## ======================================= Coverage 95.71% 95.71% ======================================= Files 42 42 Lines 2705 2709 +4 Branches 337 338 +1 ======================================= + Hits 2589 2593 +4 Misses 92 92 Partials 24 24 ``` | [Impacted Files](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/200?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer) | Coverage Δ | | |---|---|---| | [bemserver\_core/input\_output/timeseries\_io.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/200?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvaW5wdXRfb3V0cHV0L3RpbWVzZXJpZXNfaW8ucHk=) | `97.10% <100.00%> (ø)` | | | [bemserver\_core/model/timeseries.py](https://app.codecov.io/gh/BEMServer/bemserver-core/pull/200?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BEMServer#diff-YmVtc2VydmVyX2NvcmUvbW9kZWwvdGltZXNlcmllcy5weQ==) | `99.59% <100.00%> (+<0.01%)` | :arrow_up: |

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