chore!: refactor the testnode to expose the genesis state

[evan-forbes]

Overview

We need to be able to modify the genesis state when using the testnode. This PR refactors the testnode to allow for that. It also includes a helper function that handles creation of this genesis state and simplify the process of starting an in process node.

closes #1037
part of/blocking #658
spun out of and blocking #1029

Checklist

• New and updated code has appropriate documentation
• New and updated code has new and/or updated testing
• Required CI checks are passing
• Visual proof for any user facing features like CLI or documentation updates
• Linked issues closed with keywords

[rach-id]

🚀

[evan-forbes]

for posterity, the testnode code could still use some serious refactors to make it easier to understand and more useful. There's only so much we can do to make the process of starting an in process node simpler, but yeah, this is only a step in the right direction instead of a final solution.

[codecov-commenter]

Codecov Report

Merging #1038 (2738659) into main (93f2c71) will decrease coverage by 0.27%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##             main    #1038      +/-   ##
==========================================
- Coverage   51.16%   50.88%   -0.28%     
==========================================
  Files          71       71              
  Lines        4372     4398      +26     
==========================================
+ Hits         2237     2238       +1     
- Misses       1911     1936      +25     
  Partials      224      224              

Impacted Files	Coverage Δ
testutil/testnode/node_init.go	63.97% <ø> (-1.95%)	⬇️
testutil/testnode/full_node.go	62.01% <46.15%> (-13.28%)	⬇️

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