Add the jittered_expiry_policy example

[tatsuya6502]

• Add the jittered_expiry_policy_sync example.
• Add the rand crate to the development dependencies.

Fixes #453

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.25%. Comparing base (acaa5ee) to head (38fa29b).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #489      +/-   ##
==========================================
- Coverage   94.31%   94.25%   -0.07%     
==========================================
  Files          43       43              
  Lines       20492    20492              
==========================================
- Hits        19327    19314      -13     
- Misses       1165     1178      +13     

[tatsuya6502]

Merging.