samples(Storage): Add samples and tests for ObjectContext

[mahendra-google]

This PR adds three new samples and tests for Object Contexts.

storage_get_object_contexts : Retrieves the ContextsData for a specific object.

storage_list_object_contexts : Demonstrates how to iterate through and display the context metadata associated with an object.

storage_set_object_contexts: llustrates how to update or apply new context data to an existing object.

Note :- We need a new version of Google.Cloud.Storage.V1 Nuget Package which contains Filter option of ListObjectsOptions so that sample and test for List Objects with Context Data will not fail on Kokoro server. As of now I have updated Google.Cloud.Storage.V1 package version to 4.15.0 in the project file which is yet to be released.

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• storage/api/Storage.Samples/GetObjectContexts.cs:15, tag storage_get_object_contexts
• storage/api/Storage.Samples/ListObjectsWithContextFilter.cs:15, tag storage_list_object_contexts
• storage/api/Storage.Samples/SetObjectContexts.cs:15, tag storage_set_object_contexts

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[gemini-code-assist]

Code Review

This pull request introduces new sample code and unit tests for managing object contexts in Google Cloud Storage, including functionality to set, get, and list objects with context filters. Additionally, the Google.Cloud.Storage.V1 package is updated to version 4.15.0. The review feedback focuses on performance and readability improvements, specifically suggesting the removal of unnecessary list materialization when listing objects to reduce memory overhead, simplifying null-check logic using C# idioms, and clarifying documentation for filter string examples.

[gemini-code-assist]

Calling .ToList() materializes the entire collection of objects in memory. For buckets with a large number of objects, this can lead to high memory consumption and performance issues. Since the method returns an IEnumerable<Object> and the subsequent code iterates over it, you can remove .ToList() to take advantage of deferred execution and stream the results from the API. This will make the sample more efficient and scalable.

        var objects = storage.ListObjects(bucketName, prefix: null, new ListObjectsOptions { Filter = filter, Fields = "items(name,contexts)" });

[gemini-code-assist]

The condition to check if contextsData.Custom is null or empty can be written more concisely using the null-conditional (?.) and null-coalescing (??) operators. This improves readability and is a common C# idiom.

        if ((contextsData?.Custom?.Count ?? 0) == 0)

[gemini-code-assist]

The example filter strings in the documentation contain unnecessary backslashes and are wrapped in quotes, which can be confusing. To improve clarity, please remove the backslashes and the outer quotes from the examples.

    /// <param name="filter">The metadata context filter (e.g. contexts."KEY":*, -contexts."KEY":*, contexts."KEY"="VALUE", -contexts."KEY"="VALUE").</param>