WIP: Ecoflow River3+ and Delta3+ support

[ykuksenko]

Attempting to add EcoFlow support in response to #2735. Specifically Delta 3 Plus and River 3 Plus models.

Working:

• Basic status works (charging, discharging, online, onbattery, ...).
• Charge level works.
• Discharge limit from app shows correctly. Load turns off at battery.low with current mapping.

Not working:

• Any sort of control does not seem to work for load or beeper/light. Or I do not understand how to do it.

Model differences:

• Delta 3 Plus (firmware V6.31.48.29):
  • Has a beeper; it does not trigger on power loss.
  • Seems to lose USB connection randomly, needing to replug and/or restart software. (Both upsc and usbhid-scripts saw this)
• River 3 Plus (firmware V1.32.75.41):
  • Has a light instead of beeper; it does trigger on power loss.
  • Did not see USB connection issues on River 3 Plus but did less testing with it.

Attribute Details/Questions:

1. Where should the HU_FLAG_QUICK_POLL flag be used? The boolean values all seem to be alarm and status related. Does this look okay?
2. Code comments show attempted commands to control beeper and load. Please correct if I missed something there.
3. DesignCapacity and FullChargeCapacity metrics seem to be percent. Are the mappings okay to use despite NUT docs wanting these in Ah?
4. flow.[4].configactivepower attribute is close to unit Wh ratings. It matches on Delta 3+ but is not correct for River 3+. What should Wh metrics be mapped to if anything? Maybe use to calculate/estimate DesignCapacity/FullChargeCapacity.
5. RemainingCapacityLimit attribute shows the percentage at which the load will be turned off. Is this okay to map to battery.low? It is definitely a useful thing to have, just not sure if with that mapping.
6. RunTimeToEmpty does not take RemainingCapacityLimit in to account. How should the user be informed of this? The unit is in minutes, does this need to be converted to seconds or can it be left as is?

---

General points

• Described the changes in the PR submission or a separate issue, e.g.
  known published or discovered protocols, applicable hardware (expected
  compatible and actually tested/developed against), limitations, etc.

• There may be multiple commits in the PR, aligned and commented with
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  of "real" changes in the other commits. Similarly for typo fixes in
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Frequent "underwater rocks" for driver addition/update PRs

• Revised existing driver families and added a sub-driver if applicable
  (nutdrv_qx, usbhid-ups...) or added a brand new driver in the other
  case.

• Did not extend obsoleted drivers with new hardware support features
  (notably blazer and other single-device family drivers for Qx protocols,
  except the new nutdrv_qx which should cover them all).

• For updated existing device drivers, bumped the DRIVER_VERSION macro
  or its equivalent.

• For USB devices (HID or not), revised that the driver uses unique
  VID/PID combinations, or raised discussions when this is not the case
  (several vendors do use same interface chips for unrelated protocols).

• For new USB devices, built and committed the changes for the
  scripts/upower/95-upower-hid.hwdb file

• Proposed NUT data mapping is aligned with existing docs/nut-names.txt
  file. If the device exposes useful data points not listed in the file, the
  experimental.* namespace can be used as documented there, and discussion
  should be raised on the NUT Developers mailing list to standardize the new
  concept.

• Updated data/driver.list.in if applicable (new tested device info)

Frequent "underwater rocks" for general C code PRs

• Did not "blindly assume" default integer type sizes and value ranges,
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• For newly added files, the Makefile.am recipes were updated and the
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General documentation updates

• Updated docs/acknowledgements.txt (for vendor-backed device support)

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Additional work may be needed after posting this PR

• Propose a PR for NUT DDL with detailed device data dumps from tests
  against real hardware (the more models, the better).

• Address NUT CI farm build failures for the PR: testing on numerous
  platforms and toolkits can expose issues not seen on just one system.

• Revise suggestions from LGTM.COM analysis about "new issues" with
  the changed codebase.
  LGTM.COM looks to be shutdown as of Dec 16 (2022?).*