Columnar query engine filter handle == null filters

[albertlockett]

part of #1508

Handles filter predicates like severity_text == null or attributes["x"] == null (e.g. doesn't exist) when filtering using the columnar query engine.

It handles all the cases, including when the optional column is not present, when then the ID column (used to join attributes) is not present or null (meaning no attributes), and when attribute batches are entirely absent.

[codecov]

Codecov Report

❌ Patch coverage is 94.30380% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.51%. Comparing base (dfca971) to head (b0bd265).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1538      +/-   ##
==========================================
+ Coverage   83.50%   83.51%   +0.01%     
==========================================
  Files         428      428              
  Lines      119410   119720     +310     
==========================================
+ Hits        99713    99990     +277     
- Misses      19163    19196      +33     
  Partials      534      534              

Components	Coverage Δ
otap-dataflow	84.68% <ø> (-0.03%)	⬇️
query_abstraction	80.61% <ø> (ø)
query_engine	90.30% <94.30%> (+0.03%)	⬆️
syslog_cef_receivers	∅ <ø> (∅)
otel-arrow-go	53.50% <ø> (ø)

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