Remove json dependency

[BenediktBurger]

• Removes dependency on jsonrpc2-objects and jsonrpc2-pyclient. These two dependencies can be written in two small files, which enables us to support older versions of Python than the dependencies allow.
• Adds a small version of RPCServer for use in Python<3.9 instead of the version of openrpc package. This self written version does not yet support fully openrpc creation of method description, therefore it is good to keep openrpc as a dependency for those python versions, where it is available.

Closes #5

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.10345% with 18 lines in your changes are missing coverage. Please review.

Project coverage is 87.63%. Comparing base (4cc7cca) to head (549f628). Report is 2 commits behind head on main.

Files	Patch %	Lines
pyleco/json_utils/rpc_server_definition.py	84.81%	7 Missing and 5 partials :warning:
pyleco/json_utils/errors.py	88.88%	4 Missing :warning:
pyleco/coordinators/coordinator.py	84.61%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #63 +/- ## ========================================== + Coverage 87.28% 87.63% +0.35% ========================================== Files 33 36 +3 Lines 2626 2846 +220 Branches 314 343 +29 ========================================== + Hits 2292 2494 +202 - Misses 280 293 +13 - Partials 54 59 +5 ``` | [Flag](https://app.codecov.io/gh/pymeasure/pyleco/pull/63/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/63/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymeasure) | `87.63% <93.10%> (+0.35%)` | :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]

Working for a week in the lab.

[bilderbuchi]

• Removes dependency on jsonrpc2-objects and jsonrpc2-pyclient. These two dependencies can be written in two small files, which enables us to support older versions of Python than the dependencies allow.

  • Adds a small version of RPCServer for use in Python<3.9 instead of the version of openrpc package. This self written version does not yet support fully openrpc creation of method description, therefore it is good to keep openrpc as a dependency for those python versions, where it is available.

Closes #5

A few thoughts from skimming the PR:

• I would caution against supporting py37, as it has been EOL since last year. Py38 follows this year.
• The package metadata has requires-python = ">=3.9", so installation should not be possible on lower Python versions anyway. I guess you need py38, nevertheless?
• It's good that you restricted the self-written code to just use it when necessary, as it's easier to remove later, and reduce maintenance burden.

[BenediktBurger]

Thanks for your comments

* I would caution against supporting py37, as it has been EOL since last year. Py38 follows this year.

The idea was, to include pyleco into pymodaq, which supports python 3.8 and @seb5g mentioned, that he would like to use it on an old system, which only allows python 3.7. However, I noticed, that python 3.7 is not achievable in #61 , so I dropped that idea.

* The package metadata has `requires-python = ">=3.9"`, so installation should not be possible on lower Python versions anyway. I guess you need py38, nevertheless?

This PR is the first one of two, which adds objects. The second one (#64 ) with more changes, changes also that requirement.

* It's good that you restricted the self-written code to just use it when necessary, as it's easier to remove later, and reduce maintenance burden.

Especially as it is not as complete as the imported code.