Sdm-modbus

* **Warning:** renamed various p1/p2/p3 registers to conform to industry wide convention to use l1/l2/l3.
* **New devices:** Garo GNM3D-RS485 (thanks ksjoberg) and a ESP2866/ESP32 based DSMR 5.0 P1 meter.
* Fixed inherited parent connection unit logic.
* Switched to poetry build system. (thanks ksjoberg)
* Added testing framework. (thanks ksjoberg)
* Scaling informating added to register maps, usable by adding `scaling=True` to `read_all()` or `read()` functions.
* Extended SDM72 registers, PR 11. (thanks thokis)

* added support for sdm72d-m (6, thanks bartv)
* added power factor and a number of energy registers for sdm630
* cleaned up and fixed various project packaging files

- Added parent connection re-use
- Reconnect on stale connection when using `pymodbus` 2.5.0
- Version bump to `pymodbus` requirement

- fix fatal error in parity parameter parsing (thanks to jglazko)

- Fix missing batch value for sdm230 running_time holding register

- Added support for SDM230