Add Tests for `XRPPayIDClient`

[keefertaylor]

High Level Overview of Change

Add additional tests for XRPPayIDClient

Context of Change

This change brings us to testing parity with the other SDK tests (ex: Xpring-JS tests).

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Refactor (non-breaking change that only restructures code)
• [x] Tests (You added tests for code that already exists, or your new feature included in this PR)
• [ ] Documentation Updates
• [ ] Release

Before / After

PayIDClient is now sufficiently tested.

Test Plan

CI

[codecov[bot]]

Codecov Report

Merging #252 into master will increase coverage by 0.31%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #252      +/-   ##
==========================================
+ Coverage   89.69%   90.01%   +0.31%     
==========================================
  Files          42       42              
  Lines         941      941              
==========================================
+ Hits          844      847       +3     
+ Misses         97       94       -3     

Impacted Files	Coverage Δ
XpringKit/PayID/XRPPayIDClient.swift	85.00% <100.00%> (ø)
XpringKit/PayID/PayIDClient.swift	100.00% <0.00%> (+3.44%)	:arrow_up:

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