add tests & refactor tx crate - alt

[tzemanovic]

Describe your changes

an alternative to #3835 (without the refactor of tx sections access 9842883, which breaks compatibility with hermes/gaia in a way I don't yet understand)

related to #1497

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:

[codecov]

Codecov Report

Attention: Patch coverage is 81.89386% with 174 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@4110d8f). Learn more about missing BASE report.
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/tx/src/section.rs	69.00%	137 Missing ⚠️
crates/tx/src/sign.rs	80.99%	23 Missing ⚠️
crates/tx/src/types.rs	98.39%	6 Missing ⚠️
crates/node/src/shell/finalize_block.rs	37.50%	5 Missing ⚠️
crates/node/src/shell/mod.rs	33.33%	2 Missing ⚠️
crates/node/src/shell/prepare_proposal.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3868   +/-   ##
=======================================
  Coverage        ?   73.20%           
=======================================
  Files           ?      341           
  Lines           ?   105183           
  Branches        ?        0           
=======================================
  Hits            ?    76994           
  Misses          ?    28189           
  Partials        ?        0           

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[mergify]

Hey @tzemanovic, your pull request has been dequeued due to the following reason: CHECKS_FAILED.
Sorry about that, but you can requeue the PR by using @mergifyio requeue if you think this was a mistake.

[tzemanovic]

@Mergifyio requeue

[mergify]

requeue

✅ The queue state of this pull request has been cleaned. It can be re-embarked automatically