ci: make package test failures fail the build, cover four untested packages

[pyramation]

Summary

The test job in ci.yml carried a job-level continue-on-error: true, so a failing package test surfaced as a red check but left the workflow conclusion green — nothing blocked a merge. That is how the object-tree set_and_commit / set_many_and_commit verify+revert signature bug (fixed in #115) reached main: the deployed functions take a defaulted message text argument that the verify scripts omitted, so ::regprocedure could not resolve them.

   test:
     runs-on: ubuntu-latest
-    continue-on-error: true
     strategy:
       fail-fast: false     # unchanged: one red package still lets the others report

fail-fast: false stays, so a single failure still doesn't cancel the sibling shards — it just stops being advisory.

The matrix also predates four packages that have __tests__/ and a test script, so their unit tests never ran anywhere (only integration-test's deploy→verify→revert cycle touched them):

+ inflection-db   1 suite,  29 tests
+ object-store    6 suites, 28 tests
+ object-tree     7 suites, 14 tests
+ partman         1 suite,   2 tests

All four pass locally against constructiveio/postgres-plus:18, which is why they are safe to make blocking in the same PR.

Finally, both workflows ran pnpm -r build between pnpm install and the database setup. No package in this workspace declares a build script, so pnpm 9 prints None of the selected packages has a "build" script and moves on, while pnpm 10+ treats it as an error — a latent break on the next toolchain bump, and dead time on every run today. Dropped from ci.yml and integration-test.yml.

Verification

• npx jest in each of packages/{inflection-db,object-store,object-tree,partman} — green (counts above).
• Confirmed no "build" script exists in the root manifest or any packages/*/package.json before removing the step.

Link to Devin session: https://app.devin.ai/sessions/43b0b10711174fa49d51907bf2b0c25f
Requested by: @pyramation

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