Fix imports broken by moved re-exports in Rust examples

[jdisanti]

Existing Example Update

The submitter has:

• Confirmed that the correct copyright is included in all files.
• Major code changes have been reviewed, and the submitter has incorporated review comments.
• Changed or added comments and strings have been reviewed, and the submitter has incorporated any and all suggested edits.

Description of Changes

A breaking change is being made for the next version of the Rust SDK: smithy-lang/smithy-rs#1085

This PR updates the examples to successfully compile after that breaking change.

• I have tested my changes and created unit tests for new code paths.
• Changes have been reviewed, and all reviewer comments have been incorporated.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.