Issue number: closes #7915

Summary

This PR adds documentation for two new Lambda features: Lambda Managed Instances and Durable Functions.

Changes

I created a new lambda-features section in the docs with two pages:

Lambda Managed Instances

• Explains the multi-process concurrency model used by Python runtime
• Shows how each Powertools utility works (Logger, Tracer, Metrics, Parameters, Idempotency, Batch)
• FAQ addressing common questions about cache behavior, thread safety, etc.

Durable Functions

• Documents the native integration between Powertools Logger and the Durable Execution SDK via context.set_logger()
• Explains log deduplication during replays
• Shows how to use Tracer, Metrics, Idempotency, Parser, and Parameters
• Clarifies when to use Powertools Idempotency vs built-in step idempotency (ESM triggers, methods you don't want as steps)

The idea here is to create those pages as integration guides, not feature documentation. They follow a different structure than core utilities because:

1/ The focus is "how Powertools works with X" rather than "how to use Powertools feature Y"
2/ Current customers that users Powertools should find guidance on Powertools compatibility with those new features
3/ The content is more about considerations and gotchas than step-by-step tutorials

User experience

Please share what the user experience looks like before and after this change

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