Implemented a Clock interface that is used instead of time.Now to aid testing

[kelvinmwinuka]

…d time.After are used.

[codecov]

Codecov Report

Attention: Patch coverage is 88.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 59.81%. Comparing base (6e51097) to head (25ffb30).
Report is 1 commits behind head on main.

Files	Patch %	Lines
pkg/echovault/keyspace.go	0.00%	1 Missing and 1 partial ⚠️
pkg/echovault/echovault.go	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   59.76%   59.81%   +0.04%     
==========================================
  Files          31       31              
  Lines        5831     5838       +7     
==========================================
+ Hits         3485     3492       +7     
  Misses       2046     2046              
  Partials      300      300              

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