Migrate API v1 simulation services to centralized observability

[anth-volk]

Summary

Migrate the API v1 simulation entry, Modal gateway, executor, and batch workers to policyengine-observability 2.0 and central Google Cloud telemetry.

Scope

• Replace version 1 global helpers with runtime-bound operations and spans.
• Remove Logfire initialization, secrets, dependencies, and forced OpenTelemetry disablement.
• Carry allowlisted request and trace correlation metadata from entry to gateway to worker.
• Configure explicit service identity, environment, collector endpoint, Google project, and Workload Identity Federation credentials for approved API v1 applications.
• Add service-level failure-isolation tests.
• Keep other PolicyEngine applications outside this change.

Acceptance criteria

• Each participating service emits the version 2 structured log schema.
• Worker operations restore incoming correlation metadata without including simulation inputs or reform payloads.
• No Logfire runtime path remains in these services.
• Failed telemetry setup or export does not change simulation outcomes.
• Relevant formatting, lint, unit, integration, and deployment configuration checks pass.