Add concat and split methods for Uint without complicated type bounds

[andrewwhitehead]

Related to #1095

[codecov]

Codecov Report

❌ Patch coverage is 97.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.97%. Comparing base (ac719ef) to head (b525af2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/uint/concat.rs	97.77%	1 Missing ⚠️
src/uint/split.rs	97.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1223      +/-   ##
==========================================
+ Coverage   87.94%   87.97%   +0.03%     
==========================================
  Files         184      184              
  Lines       21165    21238      +73     
==========================================
+ Hits        18613    18684      +71     
- Misses       2552     2554       +2     

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