Improved error handling and diagnostics

[covert-encryption]

• Uses the newly added additional exception types, minor changes to prior PR
• CLI exit status codes are a bit more specific, numbers changed
• CLI prints the help and exits with status 1 on invalid argument values
• Tests changed accordingly

[codecov[bot]]

Codecov Report

Merging #92 (71d5a6d) into main (e0a52fc) will increase coverage by 0.09%. The diff coverage is 96.15%.

@@            Coverage Diff             @@
##             main      #92      +/-   ##
==========================================
+ Coverage   79.13%   79.22%   +0.09%     
==========================================
  Files          35       35              
  Lines        2727     2739      +12     
  Branches      620      624       +4     
==========================================
+ Hits         2158     2170      +12     
- Misses        432      433       +1     
+ Partials      137      136       -1     

Impacted Files	Coverage Δ
covert/cli/dec.py	74.37% <66.66%> (ø)
covert/blockstream.py	89.42% <100.00%> (ø)
covert/cli/__main__.py	95.83% <100.00%> (+1.38%)	:arrow_up:
covert/cli/enc.py	79.47% <100.00%> (ø)
covert/exceptions.py	100.00% <100.00%> (ø)
covert/pubkey.py	88.48% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update e0a52fc...71d5a6d. Read the comment docs.