Batch events tests (backport #3857)

[mergify]

Describe your changes

Partially addresses #3828.

• Adds unit tests for gas payment with whitelisted, non-native token
• Adds unit tests for batched txs' events
• Removes the unused Success event
• Misc refactor of tx signatures in unit tests

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 #3857 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.04%. Comparing base (e1983f2) to head (9cf0f07).
Report is 11 commits behind head on 0.44.0.

Additional details and impacted files

@@           Coverage Diff           @@
##           0.44.0    #3861   +/-   ##
=======================================
  Coverage   73.03%   73.04%           
=======================================
  Files         340      340           
  Lines      104816   104782   -34     
=======================================
- Hits        76552    76534   -18     
+ Misses      28264    28248   -16     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.