[azure-core] Search for charset detection library at import time

[yuliy-openai]

Description

The AioHttpTransport class would try to import cchardet every time it got a request where it wanted to use charset detection on an http response. This requires syscalls to look for the module, which in the case of something which makes heavy use of, say, the Cosmos SDK, adds up to a lot of resource utilization. Doing it once is faster. I opted to keep the old behavior of erroring out only when this code is called.

This was a regression from #21520

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

Thank you for your contribution @yuliy-openai! We will review the pull request and get back to you soon.

[Copilot]

Pull Request Overview

This PR optimizes the charset detection library import strategy in the AioHttpTransport class by moving import attempts from request-time to module-import-time, reducing syscall overhead for applications making frequent HTTP requests.

• Moves charset detection library imports (cchardet, chardet, charset_normalizer) from the text() method to module-level
• Creates a fallback detect function that preserves the original error behavior when no charset libraries are available
• Updates the CHANGELOG to document this performance fix

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
sdk/core/azure-core/azure/core/pipeline/transport/_aiohttp.py	Moves charset detection imports to module level and simplifies the text() method
sdk/core/azure-core/CHANGELOG.md	Documents the bug fix for repeated import attempts

[annatisch]

Thanks @yuliy-openai - could you please agree to the CLA policy above?

[pvaneck]

LGTM. Thank you!

[yuliy-openai]

could you please agree to the CLA policy above?

I'm still chasing down our legal team for that :-(

[yuliy-openai]

@microsoft-github-policy-service agree company="OpenAI"

[annatisch]

/check-enforcer override

[yuliy-openai]

Thanks for your help and patience, @annatisch!

[annatisch]

You're welcome! Thank you for your contribution!