Add count_at_time function to SqLiteKeyPackageStorage

[tomleavy]

Description of changes:

Added a function that will tell you how many key packages that are held in storage will remain at a specific time in the future. This is useful in order to preemptively maintain a pool of key packages before they expire on a DS.

Testing:

Added a test to cover this functionality.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.17%. Comparing base (df87607) to head (a7b9887).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #208   +/-   ##
=======================================
  Coverage   90.16%   90.17%           
=======================================
  Files         175      175           
  Lines       31421    31448   +27     
=======================================
+ Hits        28332    28359   +27     
  Misses       3089     3089           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.