Fix broken sync json parsing and harmonize file reading

[scovich]

It turned out the sync reader was not being exercised by basic read tests. Enabling it exposed a broken json parsing algo that had already been fixed in the default reader.

Factor out the json parsing to a shared function that both engines can use.

While we're at it, factor out sync reader logic that both parquet and json readers can use.

Update the basic read unit tests to use both readers.

Fixes #372

Relevant upstream feature request: apache/arrow-rs#6522

[codecov]

Codecov Report

Attention: Patch coverage is 86.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 76.83%. Comparing base (092ee67) to head (f095b71).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
kernel/src/engine/arrow_utils.rs	86.58%	1 Missing and 10 partials ⚠️
kernel/src/engine/sync/mod.rs	84.61%	0 Missing and 6 partials ⚠️
kernel/src/engine/sync/json.rs	83.33%	0 Missing and 2 partials ⚠️
kernel/src/engine/sync/parquet.rs	81.81%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #373      +/-   ##
==========================================
+ Coverage   76.55%   76.83%   +0.27%     
==========================================
  Files          45       47       +2     
  Lines        9375     9418      +43     
  Branches     9375     9418      +43     
==========================================
+ Hits         7177     7236      +59     
+ Misses       1799     1789      -10     
+ Partials      399      393       -6     

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[scovich]

This is just an indentation change. Review with whitespace changes hidden if you're seeing this comment:

[hntd187]

LGMT

[nicklan]

lgtm, just had one small suggestion. thanks for the fixes!

[zachschuermann]

ahh nick beat me lgtm haha