ActiveJob rework #2932

Make ActiveJob the primary background-job integration in sentry-rails: one code path for every ActiveJob adapter (SolidQueue, GoodJob, Sidekiq+ActiveJob, future adapters). Backend gems enrich it through a public extension registry instead of replacing it.

Status

• Shipped in 6.7.0: producer/consumer queue spans, distributed tracing, messaging data, SolidQueue support, shared ActiveJob spec suite.
• Next: extension registry, Sidekiq on the ActiveJob path, GoodJob test coverage.

Rollout

• 7.x: opt-in per adapter via config.rails.skippable_job_adapters. Opting in may only add data, never change what's already sent.
• 8.0.0: ActiveJob-first by default for Sidekiq, aligned with the Sentry queues spec, with a migration guide.
• Unchanged: raw Sidekiq/Resque/DelayedJob jobs and non-Rails apps keep their native integrations.
• Maintenance-only: Resque and DelayedJob.

Out of scope: cron monitoring for SolidQueue/GoodJob, Sidekiq-specific features, queue profiling (#2045), Shoryuken (#2237).