docs: clarify thread safety of service resolution in .NET dependency …

[abhiramch018]

…injection

Summary

Clarified that resolving services from the built-in .NET dependency injection (DI) container is thread-safe.

Changes

• Updated the Thread safety section in dependency-injection-guidelines.md.
• Added explicit statement that:
  • Service resolution via IServiceProvider and IServiceScope is thread-safe.
  • Service implementations themselves must still handle internal concurrency.
• Added a note block for clarity.

Motivation

Resolves issue #47086 by explicitly documenting DI service resolution thread safety, which was previously implied but not stated.

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

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docs/core/extensions/dependency-injection-guidelines.md	Dependency injection guidelines