Add skipping output

[abbiemery]

This is an option for propagation of skipped devices. It is not particularly elegant, but it does avoid changing the event routing or anything vital for now until we find a better option that we are happy with and that is optimal.

[abbiemery]

Don't worry, tests are coming. Will make a note in the dev docs though. There is a doc for how updates aree scheduled but i'll update it.

[codecov[bot]]

Codecov Report

Patch coverage: 89.47% and project coverage change: +0.03% :tada:

Comparison is base (04a0c47) 94.65% compared to head (dbda9ab) 94.68%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #180 +/- ## ========================================== + Coverage 94.65% 94.68% +0.03% ========================================== Files 41 41 Lines 1309 1318 +9 ========================================== + Hits 1239 1248 +9 Misses 70 70 ``` | [Files Changed](https://app.codecov.io/gh/dls-controls/tickit/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dls-controls) | Coverage Δ | | |---|---|---| | [src/tickit/core/management/schedulers/base.py](https://app.codecov.io/gh/dls-controls/tickit/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dls-controls#diff-c3JjL3RpY2tpdC9jb3JlL21hbmFnZW1lbnQvc2NoZWR1bGVycy9iYXNlLnB5) | `94.44% <77.77%> (-3.52%)` | :arrow_down: | | [src/tickit/core/management/ticker.py](https://app.codecov.io/gh/dls-controls/tickit/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dls-controls#diff-c3JjL3RpY2tpdC9jb3JlL21hbmFnZW1lbnQvdGlja2VyLnB5) | `100.00% <100.00%> (+3.84%)` | :arrow_up: | | [src/tickit/core/typedefs.py](https://app.codecov.io/gh/dls-controls/tickit/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dls-controls#diff-c3JjL3RpY2tpdC9jb3JlL3R5cGVkZWZzLnB5) | `97.77% <100.00%> (+0.27%)` | :arrow_up: |

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[abbiemery]

@callumforrester , @DiamondJoseph as requested, the issue to add further testing #183 .

[abbiemery]

@callumforrester , @DiamondJoseph as requested, the issue to add further testing #183 .

@callumforrester no need for #184 , I'll roll them together.