Implement Encoding for Int Aliases

[ycscaly]

This PR adds a missing functionality for Ixxx types by implementing the Encoding trait.

Work originally done by @erik-3milabs

[codecov]

Codecov Report

❌ Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.70%. Comparing base (7ba1398) to head (4d07bdb).

Files with missing lines	Patch %	Lines
src/int/encoding.rs	0.00%	18 Missing ⚠️
src/int/macros.rs	0.00%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #990      +/-   ##
==========================================
- Coverage   79.86%   79.70%   -0.17%     
==========================================
  Files         163      164       +1     
  Lines       17593    17630      +37     
==========================================
+ Hits        14051    14052       +1     
- Misses       3542     3578      +36     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[erik-3milabs]

I seem to recall that this code does not adhere to signed integer (de)serialization standards. In fact, I seem to recall this being rejected last year when introducing Int initially.

[ycscaly]

I seem to recall that this code does not adhere to signed integer (de)serialization standards. In fact, I seem to recall this being rejected last year when introducing Int initially.

@tarcieri what changes are needed for this to be accepted? Currently this very important functionality is missing.