refactor: lazy-load azurefunctions.extensions.base for Python 3.13+

[gavin-aguiar]

Description

Defers the import of azurefunctions.extensions.base on the v2 runtime cold path so apps that don't use deferred bindings or HTTP v2 don't pay the cost. This recovers roughly 170–200 ms of cold-start time on Python 3.13+ Flex Consumption.

Validation

• Cold-start profile on Flex Consumption mesh container (Python 3.13, real production image) measured with PYTHONPROFILEIMPORTTIME=1:

Profile	Total cumulative imports	Notes
Before	608 ms	6 azurefunctions.extensions.base.* modules in report (~260 ms cumulative)
After	355 ms	Zero azurefunctions.extensions.base.* modules

Fixes #

---

Pull Request Checklist

Host-Worker Contract

• Does this PR impact the host-worker contract (e.g., gRPC messages, shared interfaces)?
  • If yes, have the changes been applied to:
    • azure_functions_worker (Python <= 3.12)
    • proxy_worker (Python >= 3.13)
  • If no, please explain why:

Worker Execution Logic

• Does this PR affect worker execution logic (e.g., function invocation, bindings, lifecycle)?
  If yes, please answer the following:

Python Version Coverage

• Does this change apply to both Python <=3.12 and 3.13+?
• If yes, have the changes been made to:
  • azure_functions_worker (Python <= 3.12)
  • runtimes/v1 / runtimes/v2 (Python >= 3.13)
• If no, please explain why:

Programming Model Compatibility (for Python 3.13+)

• Does this change apply to both:
  • V1 programming model (runtimes/v1)?
  • V2 programming model (runtimes/v2)?
• Explanation (if limited to one model):