fix: update test operation generator to find any operation in the service closure

[mcmasn-amzn]

Motivation and Context

When using operations nested under resources, the current search will raise "NoSuchElementException". This fixes the search to include all operations within the service closure

Description

The error is visible in client generates like this:

Projection rust-client failed: java.util.NoSuchElementException: Collection contains no element matching the predicate.
java.util.NoSuchElementException: Collection contains no element matching the predicate.
        at software.amazon.smithy.rustsdk.endpoints.OperationInputTestGeneratorKt.operationId(OperationInputTestGenerator.kt:242)
        at software.amazon.smithy.rustsdk.endpoints.OperationInputTestGenerator$operationInvocation$1.invoke(OperationInputTestGenerator.kt:183)
        at software.amazon.smithy.rustsdk.endpoints.OperationInputTestGenerator$operationInvocation$1.invoke(OperationInputTestGenerator.kt:180)

Testing

gradle :aws:sdk-codegen:check

Checklist

• For changes to the smithy-rs codegen or runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "client," "server," or both in the applies_to key.
• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

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[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[landonxjames]

Canary run: https://github.com/smithy-lang/smithy-rs/actions/runs/12243815464

[landonxjames]

Having to use a Smithy index like this instead of just iterating through all the operations is a bit of a smithy footgun and I think there are probably several other places in the codebase that do this. Thanks for catching it and providing the test!

[mcmasn-amzn]

Thanks @landonxjames. Yes, I wrote the original code here in 2023 and didn't realize serviceShape.allOperations doesn't recurse through attached resources. It's a surprising behavior, but also, one that's probably tricky to fix without breaking existing callers.

[landonxjames]

Canary passed and the semver test failure is currently expected, merging