Fix deterministic codegen check for `SmokeTestsDecorator` (#3809)

## Motivation and Context
Attempts to fix [a release
blocker](https://github.com/smithy-lang/smithy-rs/actions/runs/10601508703/job/29381493978)

## Description
This PR ensures that `SmokeTestsDecorator` renders test functions into
`smoketests` in a consistent order, e.g. sorted first by operation name
and then within that operation, sorted by test case ID.

## Testing
- [x] Existing tests in CI (specifically `check-deterministic-codegen`)

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