fix: StaticArrayVal payload encoding, improve roundtrip checker

[aborgna-q]

The eager encoding of StaticArrayVal's payload caused the nested values to be encoded as escaped strings, causing errors on the rust decoder.

This PR rollbacks the changes to StaticArrayVal done in #2436 and adds a better workaround in the roundtrip test instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.03%. Comparing base (ce5a763) to head (e62f3ad).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2444   +/-   ##
=======================================
  Coverage   82.03%   82.03%           
=======================================
  Files         247      247           
  Lines       46018    46018           
  Branches    41608    41608           
=======================================
  Hits        37749    37749           
  Misses       6250     6250           
  Partials     2019     2019           

Flag	Coverage Δ
python	85.26% <ø> (ø)

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