Fix missing handling for operator usage in Materialized queries

[Ngalstyan4]

Fixes #227

[github-actions]

Benchmarks

metric	old	new	pct change
recall (after create)	0.740	0.740	-
recall (after insert)	0.784	0.778	-0.77%
select bulk tps	477.403	498.118	+4.34%
select bulk latency (ms)	16.097	15.843	-1.58%
select bulk latency (stddev ms)	3.106	1.360	-56.21%
create latency (ms)	1225.192	1227.194	+0.16%
insert bulk tps	11.208	11.058	-1.34%
insert bulk latency (ms)	89.212	90.427	+1.36%
insert bulk latency (stddev ms)	3.380	3.737	+10.56%
disk usage (bytes)	6348800.000	6348800.000	-

[codecov]

Codecov Report

Merging #228 (673f683) into main (1c2ff53) will increase coverage by 0.05%.
The diff coverage is 50.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #228      +/-   ##
==========================================
+ Coverage   78.14%   78.20%   +0.05%     
==========================================
  Files          23       23              
  Lines        1643     1647       +4     
  Branches      404      405       +1     
==========================================
+ Hits         1284     1288       +4     
- Misses        177      178       +1     
+ Partials      182      181       -1     

Files	Coverage Δ
src/hooks/plan_tree_walker.c	66.66% <50.00%> (-0.84%)	⬇️

... and 1 file with indirect coverage changes