Set 14.2.0 as upcoming version; run N-1 tests against 14.1.0

[ihalatci]

Set 14.2.0 as upcoming version

Bumps the in-development version on the release-14 line from released 14.1 to upcoming 14.2.0, and points the N-1 CI slot at 14.1.0 (previously 14.0.1). This is the direct 14.x analogue of the 13.4.0 bootstrap commit 4cd5cdde5 ("Set 13.4.0 as upcoming version; run N-1 tests against 13.3.0") and follows the same canonical 12-file pattern.

What changed (mirrors the 13.4 template exactly)

• configure.ac / configure — project version 14.1.0 → 14.2.0
• citus.control / citus_columnar.control — default_version = '14.2-1'
• config.py — MASTER_VERSION = "14.2"
• 4 new comment-only migration stubs: citus--14.1-1--14.2-1 (+ downgrade) and citus_columnar--14.1-1--14.2-1 (+ downgrade)
• multi_extension.sql / .out — 14.2-1 snapshot + downgrade blocks; SHOW citus.version → 14.2.0; DETAIL lines bumped to 14.2
• .github/workflows/build_and_test.yml — N-1 jobs now run against /opt/citus-versions/v14.1.0 / 14.1-1, stable image suffix -vf4adc47

The workflow half is byte-identical to the earlier CI-validated N-1 experiment. Its only divergence from the 13.4 template is the 5 PG-minor param bumps (16.14 / 17.10 / 18.4), which the 14.x -vf4adc47 stable images were published at.

N-1 CI expectation (pre-existing, orthogonal)

Running N-1 against 14.1.0 is expected to reproduce the latent citus #8587 gap — the same 2 deterministic check-multi-1 reds seen on 13.x (PR #8632): Lib N-1 / PG18 and Coordinator N-1 / PG18 fail on create_ref_dist_from_citus_local (delete_placement_metadata(1)); Worker N-1 and SQL N-1 pass. This was confirmed across two runs during the validation experiment (closed PR #8633) and is pre-existing / orthogonal to this version bump.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.62%. Comparing base (1c80ba2) to head (403baf6).

Additional details and impacted files

@@               Coverage Diff                @@
##           release-14.0    #8635      +/-   ##
================================================
- Coverage         88.63%   88.62%   -0.01%     
================================================
  Files               288      288              
  Lines             64116    64115       -1     
  Branches           8046     8046              
================================================
- Hits              56827    56824       -3     
- Misses             4969     4971       +2     
  Partials           2320     2320              

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