samples(storagecontrol): add delete folder recursive sample

[nidhiii-27]

This PR adds the SDK sample and tests for the hierarchical namespace recursive delete feature, resolving b/521168740.

[gemini-code-assist]

Code Review

This pull request adds a new DeleteFolderRecursive sample and integrates it into the sample runner and AutoRun test flow. A critical compilation issue was identified in the new sample: DeleteFolderRecursive().get() returns a google::cloud::Status rather than a StatusOr, so checking !deleted and calling .status() will fail to compile. The reviewer provided a code suggestion to use .ok() and throw the status directly.

[gemini-code-assist]

The DeleteFolderRecursive function returns a google::cloud::future<google::cloud::Status>. Therefore, calling .get() returns a google::cloud::Status object, not a StatusOr. Since google::cloud::Status does not have an operator bool() or a .status() method, this code will fail to compile. It should check .ok() and throw the status directly.

    auto status = client.DeleteFolderRecursive(name).get();
    if (!status.ok()) throw std::move(status);

References

1. Prefer defensive code, such as explicit ok() checks, even if they seem redundant based on the current implementation of a framework, as the framework's contract may change in the future.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.70%. Comparing base (55df15b) to head (9a1880f).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16149   +/-   ##
=======================================
  Coverage   92.70%   92.70%           
=======================================
  Files        2353     2353           
  Lines      218352   218352           
=======================================
+ Hits       202418   202425    +7     
+ Misses      15934    15927    -7     

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