EZSP v14

[puddly]

This is going to be a huge change. Very WIP, only backup and restore is working.

• The command format for sending packets seems to have changed significantly.
• Parameters for most EZSP commands have been reordered.
• The error codes returned by the firmware have also completely changed and are not compatible with previous versions.
• Nothing is documented 😄 (https://github.com/SiliconLabs/simplicity_sdk/issues/11)

[puddly]

This PR is in a state to be able to run successfully on my home network.

However, EmberZNet 8.0.0.0 is completely broken:

1. LQI and RSSI just do not contain valid values for any packet.
2. Unicast performance is abysmal and most sends do not succeed once more than a few packets have been sent at once.

This PR needs to be merged so that universal-silabs-flasher can enter the bootloader to downgrade from 8.0.0.0 but I'm otherwise not going to investigate EmberZNet 8.0.0.0 further.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.08676% with 4 lines in your changes missing coverage. Please review.

Project coverage is 99.38%. Comparing base (3657cf3) to head (52dae0b).

Files	Patch %	Lines
bellows/zigbee/application.py	92.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #631 +/- ## ========================================== - Coverage 99.72% 99.38% -0.34% ========================================== Files 75 79 +4 Lines 5017 5047 +30 ========================================== + Hits 5003 5016 +13 - Misses 14 31 +17 ```

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[puddly]

Project coverage shrinks just a little bit with this PR but unfortunately there's no sensible way to actually deal with EZSP v14 command processing without rewriting all EZSP commands to use named parameters.

[Hedda]

Also see comments by Zigbee2MQTT/zigbee-herdsman ember developer Nerivec in https://github.com/SiliconLabs/simplicity_sdk/issues/13