Fix Issue #248

[CarlosCancino-Chacon]

This pull request closes issue #248, i.e., fixes the behavior of the clip_note_off argument in slice_ppart_by_time.

The pull request consists of

• The bug fix itself
• An upgraded test checking both the clip_note_off and reindex_notes arguments of slice_ppart_by_time

[codecov-commenter]

Codecov Report

Patch coverage: 91.66% and project coverage change: +0.04 :tada:

Comparison is base (59cbe3a) 85.00% compared to head (6731eeb) 85.04%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #253 +/- ## =========================================== + Coverage 85.00% 85.04% +0.04% =========================================== Files 72 72 Lines 12653 12667 +14 =========================================== + Hits 10756 10773 +17 + Misses 1897 1894 -3 ``` | [Impacted Files](https://app.codecov.io/gh/CPJKU/partitura/pull/253?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CPJKU) | Coverage Δ | | |---|---|---| | [partitura/utils/music.py](https://app.codecov.io/gh/CPJKU/partitura/pull/253?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CPJKU#diff-cGFydGl0dXJhL3V0aWxzL211c2ljLnB5) | `74.48% <50.00%> (+0.30%)` | :arrow_up: | | [tests/test\_utils.py](https://app.codecov.io/gh/CPJKU/partitura/pull/253?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CPJKU#diff-dGVzdHMvdGVzdF91dGlscy5weQ==) | `98.13% <100.00%> (+0.12%)` | :arrow_up: |

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