PG19: stabilize columnar regression outputs

[ibrahim halatci (ihalatci)]

Closes #8732.

Summary

• pin pglz only around the heap TOAST-size assertion in columnar_insert
• extend the existing EXPLAIN normalizer for PG19 SubPlan any_N names
• add the PG19 alternate VACUUM FULL status output for columnar_vacuum_vs_insert

All three failures are PostgreSQL output/configuration drift that predates REL_19_BETA1, not Beta2 regressions or columnar compatibility defects:

• PostgreSQL 34dfca293432 made LZ4 the default TOAST compression when available
• PostgreSQL 8c49a484e8eb introduced textual subplan names such as any_1
• PostgreSQL ac58465e0618 introduced REPACK and the repacking ... in physical order wording

Direct Beta1 and Beta2 runs reproduce the same behavior for all three cases.

Tests

• PG17.10: check-columnar-minimal EXTRA_TESTS="columnar_insert columnar_chunk_filtering"; check-columnar-isolation
• PG18.4: check-columnar-minimal EXTRA_TESTS="columnar_insert columnar_chunk_filtering"; check-columnar-isolation
• PG19beta2: check-columnar-minimal EXTRA_TESTS="columnar_insert columnar_chunk_filtering"; check-columnar-isolation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.81%. Comparing base (ff8f1f8) to head (bf7ec6b).

Additional details and impacted files

@@              Coverage Diff              @@
##           pg19-support    #8734   +/-   ##
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  Coverage         88.80%   88.81%           
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  Files               288      288           
  Lines             64416    64416           
  Branches           8100     8102    +2     
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+ Hits              57206    57208    +2     
  Misses             4873     4873           
+ Partials           2337     2335    -2     

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