Old python

[BenediktBurger]

Allow Python 3.8 (previously only Python>=3.9)

• uses #63

Main changes:

• for python<3.9 use self written RPCServer instead of openrpc.
• Rename cls for TransparentDirector and Actor to device_class, as Python 3.8 does not like cls in an init.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 84.21053% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 87.65%. Comparing base (d337a29) to head (b5f29d6).

Files	Patch %	Lines
pyleco/directors/transparent_director.py	50.00%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ========================================== + Coverage 87.63% 87.65% +0.02% ========================================== Files 36 36 Lines 2846 2859 +13 Branches 343 346 +3 ========================================== + Hits 2494 2506 +12 Misses 293 293 - Partials 59 60 +1 ``` | [Flag](https://app.codecov.io/gh/pymeasure/pyleco/pull/64/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymeasure) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/pymeasure/pyleco/pull/64/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymeasure) | `87.65% <84.21%> (+0.02%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymeasure#carryforward-flags-in-the-pull-request-comment) to find out more.

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[BenediktBurger]

It worked for a week in the lab.