Prepare to support parquet row group skipping

[scovich]

In preparation for #362 that actually implements parquet row group skipping, here we make various preparatory changes that can stand on their own:

• Plumb the predicates through to the parquet readers, so that they can easily start using them
• Add and use a new Expression::is_not_null helper that does what it says
• Factor out replay_for_XXX methods, so that log replay involving push-down predicates can be tested independently.
• Don't involve .json in log replay if .checkpoint.parquet is available

This should make both changes easier to review.

[codecov]

Codecov Report

Attention: Patch coverage is 89.28571% with 12 lines in your changes missing coverage. Please review.

Project coverage is 77.06%. Comparing base (340c5e4) to head (532865f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
kernel/src/engine/default/parquet.rs	36.36%	6 Missing and 1 partial ⚠️
kernel/src/snapshot.rs	94.28%	0 Missing and 2 partials ⚠️
kernel/src/transaction.rs	93.93%	0 Missing and 2 partials ⚠️
kernel/src/scan/mod.rs	96.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #381      +/-   ##
==========================================
+ Coverage   76.86%   77.06%   +0.20%     
==========================================
  Files          47       47              
  Lines        9436     9524      +88     
  Branches     9436     9524      +88     
==========================================
+ Hits         7253     7340      +87     
- Misses       1789     1790       +1     
  Partials      394      394              

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[zachschuermann]

nice thanks ryan, really like the new replay_for_* LGTM!

[zachschuermann]

created #382

[nicklan]

lgtm! thanks

[nicklan]

so much nicer :)