Add a bunch of low hanging fruit masp tests (backport #3921)

[mergify]

Describe your changes

Increases the test coverage report in the affected files.

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

---

This is an automatic backport of pull request #3921 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

Attention: Patch coverage is 99.58848% with 1 line in your changes missing coverage. Please review.

Project coverage is 73.39%. Comparing base (1a8ca52) to head (e2b4450).
Report is 2 commits behind head on 0.44.0.

Files with missing lines	Patch %	Lines
crates/core/src/masp.rs	99.58%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           0.44.0    #3923      +/-   ##
==========================================
+ Coverage   73.26%   73.39%   +0.13%     
==========================================
  Files         341      341              
  Lines      105334   105576     +242     
==========================================
+ Hits        77168    77487     +319     
+ Misses      28166    28089      -77     

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