{Perf} Delay importing MSIAuthenticationWrapper and check_version_compatibility

[jiasli]

Description
Fix regressions introduced by

• {Core} Fix #14175: Load ALWAYS_LOADED_EXTENSIONS correctly #14180, which unconditionally imports check_version_compatibility and requests
• [Core] Fix get_token() issue in msi login and expiresIn key error in cloud shell login credentials for track 2 SDK related commands #14187, which unconditionally imports MSIAuthenticationWrapper and azure.core.credentials

This PR delays the imports and brings az version to its normal speed.

Testing Guide

# Before
> Measure-Command {az version}

TotalMilliseconds : 1132.3246

# After
> Measure-Command {az version}

TotalMilliseconds : 627.5202

[yonzhan]

add to S173

[haroldrandom]

Importing a module in a for loop is not a good practice.
How much can it benefit from importing in this for loop?

[jsntcy]

You can import module as many times as you want in one Python program, no matter what module it is. Every subsequent import after the first accesses the cached module instead of re-evaluating it. So there is no performance penalty.

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In reply to: 454774982 [](ancestors = 454774982)

[jiasli]

This is a tricky part. I just want to eliminate an extra if allowed_extensions:. Python has an import cache which will handle "import in a for loop" nicely.

[jsntcy]

[qianwens]

[jiasli]

@jsntcy, relative import it is not recommended according to PEP 8:

Absolute imports are recommended, as they are usually more readable and tend to be better behaved (or at least give better error messages)...