[Attention] Update attention imports

[MatthewBonanni]

Purpose

Now that #29342 has landed, many of the TYPE_CHECKING and lazy imports are no longer necessary. This PR updates them throughout the codebase

Test Plan

Recommend to run all CI tests (ready-run-all-tests)

Test Result

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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[gemini-code-assist]

Code Review

This pull request is a large-scale refactoring that removes lazy imports and TYPE_CHECKING blocks related to attention backends throughout the codebase. The changes are consistent and correctly applied, moving imports to the top level and updating type hints accordingly. This cleanup improves code readability and structure. I have reviewed all the changes and found no issues. The refactoring appears to be safe and well-executed.

[MatthewBonanni]

cc @mgoin

[yewentao256]

Thanks for the work! Let's run CI and see if we can pass

[hmellor]

It's worth noting that the TYPE_CHECKING guard isn't always a workaround for circular imports. It can save time at runtime by not importing heavy modules that are only used for type checking.

[LucasWilkinson]

LGTM! thanks for doing this!

[yewentao256]

LGTM, thanks for the work!

[NickLucche]

It's worth noting that the TYPE_CHECKING guard isn't always a workaround for circular imports. It can save time at runtime by not importing heavy modules that are only used for type checking.

yeah I am not really sure it was worth changing 40 files for that