Improvements to Modbus handling

[albireox]

This is a major refactor of how the Modbus and ModbusRegister classes work:

• Performance has been greatly improved, with Modbus.get_all() going from taking ~0.6 seconds to under 0.1. The main change is that the register and coil blocks are now read completely, in chunks as large as the device will accept, as opposed to before, when we would read each variable with one read command (although the connection was not closed in between).
• The caching mechanism has been improved and now works as expected. The default cache timeout is 1 second.
• The PLC variable list has been updated and now matches Felipe's list.
• Various renamings of methods and variables.
• Added a low-level modbus actor command to read/set Modbus variables (even those not defined in the PLC list).
• Improved the simulator to better handle overrides and events that trigger a change in the internal state of the context.
• Improve the engineering mode commands.
• Improve test coverage.

[codecov]

Codecov Report

Attention: Patch coverage is 81.70732% with 45 lines in your changes missing coverage. Please review.

Project coverage is 82.0%. Comparing base (d32b54c) to head (a2e6fd1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
python/lvmecp/modbus.py	77.1%	10 Missing and 12 partials ⚠️
python/lvmecp/safety.py	16.7%	4 Missing and 6 partials ⚠️
python/lvmecp/actor/commands/engineering.py	81.0%	2 Missing and 2 partials ⚠️
python/lvmecp/actor/commands/modbus.py	93.5%	2 Missing and 2 partials ⚠️
python/lvmecp/actor/actor.py	50.0%	1 Missing ⚠️
python/lvmecp/dome.py	95.7%	1 Missing ⚠️
python/lvmecp/hvac.py	50.0%	1 Missing ⚠️
python/lvmecp/module.py	90.0%	1 Missing ⚠️
python/lvmecp/plc.py	83.4%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #32      +/-   ##
========================================
+ Coverage   70.8%   82.0%   +11.2%     
========================================
  Files         18      19       +1     
  Lines        832     929      +97     
  Branches     116     134      +18     
========================================
+ Hits         589     761     +172     
+ Misses       186     103      -83     
- Partials      57      65       +8     

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