Add support for router firmware

[tl-sl]

Implement a new protocol for communicating with the builtin CLI on Silabs router firmware and integrate through out. This will allow to probe and flash router firmware

Router firmware must implement a custom CLI command bootloader reboot that calls the bootloader_rebootAndInstall api.

This has been tested both standalone and integrated with sl-web-tools.

Probe of CPC 115200 is fixed in #86, but also requires router firmware built with SL_CLI_LOCAL_ECHO: 0

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 36.36364% with 56 lines in your changes missing coverage. Please review.

Project coverage is 66.46%. Comparing base (b009196) to head (d4271df).
Report is 12 commits behind head on dev.

Files with missing lines	Patch %	Lines
universal_silabs_flasher/router.py	35.21%	46 Missing ⚠️
universal_silabs_flasher/flasher.py	27.27%	8 Missing ⚠️
universal_silabs_flasher/flash.py	33.33%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #85      +/-   ##
==========================================
+ Coverage   61.78%   66.46%   +4.68%     
==========================================
  Files          14       15       +1     
  Lines        1748     1822      +74     
==========================================
+ Hits         1080     1211     +131     
+ Misses        668      611      -57     

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[tl-sl]

Source for router firmware commands is here:
https://github.com/darkxst/silabs-firmware-builder/blob/b36248aef7b76bc1bdb549a20219474ceb4013d9/src/zigbee_router/app.c#L102