feat: add tracing channels support for preload files

[densetsuuu]

❓ Type of change

• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Adds tracing channel support for preload files, mirroring the existing pattern used for service providers. A new adonisjs.preload.import diagnostics channel is created and integrated into the PreloadsManager, allowing external tools and monitoring systems to trace preload module imports during the application start phase. Each preload import is wrapped with tracePromise, using the same hasSubscribers optimization to avoid unnecessary allocations when no subscribers are active.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[thetutlage]

Looks good. Thanks 👍🏽