test(integration): add application lifecycle fixture

[josecelano]

Summary

Add TrackerApplicationFixture for main-application integration suites. The fixture owns the isolated workspace, application container, and JobManager, then invokes the best shutdown sequence exposed by current production before releasing the workspace.

• Migrate the current metrics, UDP-policy, banning, and scaffold suites from implicit _jobs drop cleanup.
• Add focused lifecycle ordering coverage: the workspace is released only after awaited fixture shutdown.
• Reconcile Allow multiple integration tests at the main app level #1419 documentation and record the verification evidence.

Verification

• cargo test --test metrics-fixed-ports --test metrics-port-zero --test metrics-udp-error-enabled-port-zero --test metrics-udp-error-disabled-port-zero --test banning-udp-metrics-disabled-port-zero --test scaffold
• cargo test --test metrics-port-zero -- --nocapture
• cargo test --test metrics-port-zero -- --test-threads=1
• TORRUST_GIT_HOOKS_LOG_DIR=.tmp ./contrib/dev-tools/git/hooks/pre-commit.sh --format=json

Scope and Follow-up

Partially addresses #1419; it intentionally remains open.

Current server jobs can consume JobManager::wait_for_all's per-job timeout because they do not yet react to the shared cancellation token. This change makes test lifecycle ownership explicit but does not claim cooperative server completion. Production shutdown coordination is deferred to #1488 and draft PR #1993; this PR does not introduce a competing shutdown mechanism.

[Copilot]

Pull request overview

Adds an explicit main-application integration-test lifecycle fixture (TrackerApplicationFixture) so suites own their isolated workspace + application container + JobManager, and can request/await shutdown before releasing the temporary workspace (aligning with issue #1419’s execution model and verification evidence).

Changes:

• Introduces TrackerApplicationFixture to centralize integration-suite startup and awaited shutdown sequencing.
• Migrates existing main-level integration suites (metrics, UDP policy, banning, scaffold) from implicit _jobs drop cleanup to explicit fixture.shutdown().await.
• Updates test/docs guidance and issue-spec verification evidence to reflect the new lifecycle ownership model.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/common/workspace.rs	Adds TrackerApplicationFixture, workspace path access, and shared shutdown grace period used by suites.
tests/common/mod.rs	Re-exports TrackerApplicationFixture for suite consumption.
tests/scaffold.rs	Updates the scaffold sample to use the fixture and documents explicit awaited shutdown.
tests/metrics/port_zero.rs	Uses fixture and adds a focused ordering assertion that workspace cleanup occurs after awaited shutdown.
tests/metrics/fixed_ports.rs	Migrates fixed-port metrics suite to fixture lifecycle.
tests/metrics/udp_error_enabled_port_zero.rs	Migrates UDP error-policy (enabled) suite to fixture lifecycle.
tests/metrics/udp_error_disabled_port_zero.rs	Migrates UDP error-policy (disabled) suite to fixture lifecycle.
tests/banning/udp_metrics_disabled_port_zero.rs	Migrates banning suite to fixture lifecycle.
tests/AGENTS.md	Updates contributor guidance to require explicit fixture shutdown and clarifies process-global constraints.
docs/issues/open/1419-allow-multiple-integration-tests-at-main-app-level/ISSUE.md	Reconciles issue spec with current test structure and records verification evidence and lifecycle findings.
docs/issues/open/1419-allow-multiple-integration-tests-at-main-app-level/completion-plan.md	Adds/updates decision record for lifecycle fixture approach and mandatory verification protocol.

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[josecelano]

ACK af5ddb7