Enhance energy model

[dinayuil]

This pull request fixes issue #200

Proposed Changes

• Add an OFF PHY state
• Set a depletion call back to switch off (like Wifi module)
• Auto schedule to switch off based on the remaining energy (like Wifi module)
• Add a test for energy depletion
• Some refactoring for getting current value of a state

[non-det-alle]

Hi, thank you for the contribution. I like the general idea this PR, I'll get to reviewing it as soon as I have addressed the previous PRs in the backlog.

I merged the latest changes and I have hidden your comment with test results: we have a CI pipeline to take care of that without polluting the PR msg history. In the meantime you can update this PR by fixing eventual errors detected by the CI pipeline.

[dinayuil]

Merged code with recent changes from @maribu

[codecov]

Codecov Report

❌ Patch coverage is 80.99174% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.60%. Comparing base (0c073e7) to head (fe730d1).

Files with missing lines	Patch %	Lines
model/lora-radio-energy-model.cc	77.50%	9 Missing ⚠️
model/end-device-lora-phy.cc	0.00%	8 Missing ⚠️
model/class-a-end-device-lorawan-mac.cc	0.00%	4 Missing ⚠️
model/simple-end-device-lora-phy.cc	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #201      +/-   ##
===========================================
+ Coverage    84.47%   84.60%   +0.13%     
===========================================
  Files           67       68       +1     
  Lines         7016     7115      +99     
===========================================
+ Hits          5927     6020      +93     
- Misses        1089     1095       +6     

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[dinayuil]

I find one problem but not sure how to deal with it:
If the radio is in RX or TX, and the energy source depletes, we want to change the radio to OFF state. However, before switch, we also need to stop the RX or TX events.
A work-around might be add a Tag info marking the packet being incomplete.

I put a TODO comment in SwitchToOff function. Please let me know if you have ideas.

[dinayuil]

Removed the 'Auto schedule to switch off based on remaining energy' feature.

Reason: Encountered floating-point comparison issues when reaching to 0 energy, which could lead to an assert failure due to subtle inaccuracies.

This removal should not affect normal use cases because the BasicEnergySource class already includes a minimum energy threshold parameter (default value: 0.1×initialEnergy). Therefore, during normal simulation runs, the energy level will not typically reach a value close enough to zero to trigger the assert issue, and the simulation will stop safely beforehand.