fix rpc hex unmarshaling

[noot]

Closes: #508

Description

update RPC tests to unmarshal into a string for cases where the returned hex value may have an odd length

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For contributor use:

• 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.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• 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, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #529 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development     #529   +/-   ##
============================================
  Coverage        70.77%   70.77%           
============================================
  Files               41       41           
  Lines             2320     2320           
============================================
  Hits              1642     1642           
  Misses             536      536           
  Partials           142      142           

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