Fix chunk exclusion for prepared statements and dst changes

[svenklemm]

The constify code constifying TIMESTAMPTZ expressions when doing chunk exclusion did not account for daylight saving time switches leading to different calculation outcomes when timezone changes. This patch adds a 4 hour safety buffer to any such calculations.

Fixes #4707

[codecov[bot]]

Codecov Report

Merging #4720 (5db66c7) into main (5600fc0) will decrease coverage by 0.02%. The diff coverage is 90.00%.

@@            Coverage Diff             @@
##             main    #4720      +/-   ##
==========================================
- Coverage   90.92%   90.89%   -0.03%     
==========================================
  Files         224      224              
  Lines       42406    42424      +18     
==========================================
+ Hits        38556    38560       +4     
- Misses       3850     3864      +14     

Impacted Files	Coverage Δ
src/compat/compat.h	92.98% <ø> (ø)
src/planner/expand_hypertable.c	93.79% <88.23%> (-0.16%)	:arrow_down:
tsl/src/compression/api.c	95.70% <100.00%> (ø)
tsl/src/compression/compression.c	95.26% <100.00%> (+0.01%)	:arrow_up:
src/bgw/scheduler.c	81.57% <0.00%> (-3.22%)	:arrow_down:
tsl/src/nodes/data_node_dispatch.c	96.49% <0.00%> (-0.24%)	:arrow_down:
src/bgw/job.c	94.41% <0.00%> (-0.24%)	:arrow_down:
tsl/src/bgw_policy/job.c	88.11% <0.00%> (-0.05%)	:arrow_down:
tsl/src/reorder.c	85.63% <0.00%> (+0.26%)	:arrow_up:

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