Draft: reconstruct flash subs and commands

[sidey79]

• Please check if the PR fulfills these requirements

• Tests for the changes have been added / modified (needed for for bug fixes / features)
• commandref has been added / updated (needed for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bugfix (please link issue)
• Feature enhancement
• Documentation update
• Unittest enhancement
• other

• What is the current behavior?
  (You can also link to an open issue here, if this describes the current behavior)

• What is the new behavior (if this is a feature change)?

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

• Other information:

[codecov]

Codecov Report

❌ Patch coverage is 96.92533% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.31%. Comparing base (582f319) to head (73c0f8e).

Files with missing lines	Patch %	Lines
lib/FHEM/Devices/SIGNALduino/SD_Firmware.pm	90.45%	19 Missing ⚠️
...M/Devices/SIGNALduino/SD_Firmware/01_sub_avrdude.t	99.48%	1 Missing ⚠️
...SIGNALduino/SD_Firmware/02_sub_availableFirmware.t	99.65%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1347      +/-   ##
==========================================
+ Coverage   86.92%   87.31%   +0.38%     
==========================================
  Files         142      143       +1     
  Lines       10526    11031     +505     
  Branches     1701     1727      +26     
==========================================
+ Hits         9150     9632     +482     
- Misses       1376     1395      +19     
- Partials        0        4       +4     

Flag	Coverage Δ
fhem-00_SIGNALduino-5.24	47.21% <18.59%> (-1.78%)	⬇️
fhem-00_SIGNALduino-5.28	47.21% <18.59%> (-1.76%)	⬇️
fhem-00_SIGNALduino-5.32	47.78% <18.59%> (-1.21%)	⬇️
fhem-other_modules-5.24	55.19% <4.02%> (-0.23%)	⬇️
fhem-other_modules-5.28	55.19% <4.02%> (-0.27%)	⬇️
fhem-other_modules-5.32	55.12% <4.02%> (-0.22%)	⬇️
perl-modules-5.24	95.56% <96.32%> (+0.28%)	⬆️
perl-modules-5.28	95.47% <96.32%> (+0.44%)	⬆️
perl-modules-5.32	95.47% <96.32%> (+0.20%)	⬆️

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