Fix wrong memory context for allocation in op_rewrite.c

[var77]

The nodes were being allocated in MessageContext which doesn't live long enough and in some cases it was causing segfault when postgres was trying to access the nodes. Per source-code the plan tree is being allocated in PortalContext, so we also should allocate the overwritten nodes in PortalContext

[github-actions]

Benchmarks

metric	old	new	pct change
recall (after create)	0.740	0.740	-
recall (after insert)	0.756	0.756	-
select bulk tps	481.514	493.884	+2.57%
select bulk latency (ms)	15.964	15.513	-2.83%
select bulk latency (stddev ms)	3.298	2.926	-11.28%
create latency (ms)	1217.728	1191.480	-2.16%
insert bulk tps	11.006	11.393	+3.51%
insert bulk latency (ms)	90.850	87.766	-3.39%
insert bulk latency (stddev ms)	3.735	2.286	-38.80%
disk usage (bytes)	6348800.000	6348800.000	-

[codecov]

Codecov Report

Merging #231 (1407891) into main (b90926c) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #231   +/-   ##
=======================================
  Coverage   78.20%   78.20%           
=======================================
  Files          23       23           
  Lines        1647     1647           
  Branches      405      405           
=======================================
  Hits         1288     1288           
  Misses        178      178           
  Partials      181      181           

Files	Coverage Δ
src/hooks/op_rewrite.c	83.94% <100.00%> (ø)

[Ngalstyan4]

We should check and see whether the same change must be done here as well or no.

In there we a new Function Expression node.

[var77]

Sorry actually I made the change in this PR for Function Expression, the on for List Node is here