Added sqrt function to sdk.Decimal type

[sunnya97]

Square Roots are a generally very useful mathematical operation that is present in most Number types and should be present in our custom Number type of sdk.Decimal. Some examples of things it is useful for include Proportional Slashing (#5211), quadratic voting, and other social choice theory procedures (see: https://arxiv.org/pdf/1809.06421.pdf).

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Re-reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #5219 into master will increase coverage by 0.05%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #5219      +/-   ##
==========================================
+ Coverage   53.43%   53.48%   +0.05%     
==========================================
  Files         290      290              
  Lines       17714    17725      +11     
==========================================
+ Hits         9465     9480      +15     
+ Misses       7510     7504       -6     
- Partials      739      741       +2

[alessio]

Can you include in the PR's description the rationale of this change please?

[sunnya97]

Added

[alexanderbez]

ACK