test(postgresql): move DatabaseWithTablesTests off the shared public schema (weasel#407)

[jeremydmiller]

Closes #407.

Symptom

DatabaseWithTablesTests.detect_and_apply_schema_changes failed intermittently in full-suite runs, ~1 in 3–6 locally, with either:

Npgsql.PostgresException : XX000: could not open relation with OID 659774
  at Weasel.Postgresql.Tables.Table.readIndexesAsync(...) Table.FetchExisting.cs:365

Npgsql.PostgresException : 42P01: relation "public.dwt_contacts" does not exist

Reproduced on clean master. It never failed with the class run in isolation (8 filtered runs), so it was cross-collection interference, not a bug in the test's own logic.

Cause

The class is [Collection("integration")] and ResetSchema() resets its SchemaName — "integration" — but the tables were created in public:

var table = db.AddTable(new PostgresqlObjectName("public", "dwt_contacts"));

Nothing here isolates public, and at least nine other test files also write to it: PostgresqlMigratorTests, create_and_teardown_schemas, Tables/TableTests, Tables/IndexDefinitionTests, Tables/creating_tables_in_database, Tables/ForeignKeyTests, Tables/Indexes/FullTextIndexDefinitionTests, Functions/FunctionBodyTests, Views/ViewTests.

xUnit serialises a collection against itself but runs different collections in parallel, so another collection could drop objects in public mid-test:

• directly between apply and assert → 42P01
• between the pg_index catalog row being read and the relation being opened → XX000: could not open relation with OID, the classic Postgres catalog race

Change

Create the tables in integration, so ResetSchema() actually covers them. Same for the siblings dwt_users and dwt_people, which had identical exposure. A class-level comment records why, so they don't drift back.

Test-only — no product code touched.

Verification

12 consecutive full-suite runs on the exact configuration that used to fail (net10.0, case-sensitive), zero failures — against a prior rate of roughly 1 in 3–6.

Note

The broader hazard remains: tests sharing public across parallel collections is a standing source of this failure mode. Worth deciding separately whether public should be off-limits to anything that creates or drops objects.

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