Hide secret keys from string rep of a key

[mochipon]

In order to manage accidental / unintended secret_key exposures.

[codecov]

Codecov Report

Merging #4 (030e8c2) into main (97514e1) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main        #4   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          273       273           
=========================================
  Hits           273       273           

Impacted Files	Coverage Δ
pysesame3/device.py	100.00% <100.00%> (ø)
pysesame3/lock.py	100.00% <100.00%> (ø)

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