Add type annotation to container module variable

[jonathangreen]

Description

Add a type annotation (Services | None) to the _container_instance module-level variable in container.py.

Motivation and Context

Mypy intermittently complains about the type of _container_instance being None. Without an explicit annotation, mypy infers the type from the initial assignment (None), which can cause it to flag usages where the variable holds a Services instance. Adding the explicit Services | None annotation makes the intended type clear and prevents these sporadic type errors.

How Has This Been Tested?

This is a type annotation-only change with no runtime behavior change. Pre-commit hooks passed successfully.

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.04%. Comparing base (194642f) to head (bc52b67).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3042   +/-   ##
=======================================
  Coverage   93.04%   93.04%           
=======================================
  Files         480      480           
  Lines       43711    43711           
  Branches     6029     6029           
=======================================
  Hits        40669    40669           
  Misses       1972     1972           
  Partials     1070     1070           

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[dbernstein]

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