Fix flaky Mocha Postgres tests with shared Npgsql helper

[glen-84]

Summary

• Each test in the Mocha Postgres test project builds its own service provider, so EF accumulates more than twenty internal service providers across a run and throws ManyServiceProvidersCreatedWarning when a context is created past that threshold. Because it depends on test ordering and parallelism, the failure surfaced intermittently in CI (the *ServiceRegistration tests).
• Add a UseTestNpgsql options-builder helper that applies the Npgsql provider and ignores that warning, and route every context-building call site through it. This replaces the inline ignores that previously covered only some call sites.

Test plan

• Ran the test assembly with --parallel none, which forces the sequential ordering that exposes the flake: the affected tests fail before the change and pass after.

[Copilot]

Pull request overview

This PR addresses intermittent CI failures in Mocha.EntityFrameworkCore.Postgres.Tests caused by EF Core’s ManyServiceProvidersCreatedWarning being triggered (and treated as an error) when many test-created service providers accumulate during a run. It centralizes the Npgsql + warning configuration into a single helper and routes all DbContext option construction through it to eliminate ordering/parallelism-dependent flakes.

Changes:

• Added UseTestNpgsql extension methods to consistently configure the Npgsql provider and ignore CoreEventId.ManyServiceProvidersCreatedWarning.
• Updated all Postgres test call sites to use UseTestNpgsql instead of inline UseNpgsql(...) / ConfigureWarnings(...).
• Removed now-unneeded EF diagnostics using directives and duplicated inline warning suppression.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/SchedulingServiceRegistrationTests.cs	Switches test DbContext registration to the shared UseTestNpgsql helper.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/SagaStateEntityConfigurationTests.cs	Uses UseTestNpgsql for model-building context options.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/SagaServiceRegistrationTests.cs	Routes both direct options creation and DI registration through UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/PostgresSchedulingIntegrationTests.cs	Replaces duplicated inline warning suppression with UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/PostgresSagaStoreTests.cs	Uses UseTestNpgsql for DbContext creation in saga store setup.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/PostgresOutboxIntegrationTests.cs	Consolidates DbContext configuration via UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/PostgresMessageOutboxTests.cs	Updates all DbContextOptionsBuilder usage to UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/PostgresMessageInboxTests.cs	Updates DbContext options creation to use UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/OutboxServiceRegistrationTests.cs	Uses UseTestNpgsql and removes inline warning suppression.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/OutboxEntityConfigurationTests.cs	Uses UseTestNpgsql for design-time model creation.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/InboxServiceRegistrationTests.cs	Switches DbContext registration to UseTestNpgsql.
src/Mocha/test/Mocha.EntityFrameworkCore.Postgres.Tests/Helpers/TestDbContextOptionsBuilderExtensions.cs	Introduces the shared UseTestNpgsql helper (generic + non-generic overloads) and central warning suppression.

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