Remove Image API-related methods and tests

Deleted the ImagesApiTest class from tests and the image generation methods from the OpenAiClient class as the Image API is planned to be removed and thus no longer necessary to support in this package. The reduction in complexity will facilitate future maintenance of the package.

src/OpenAI.ChatGpt/OpenAiClient.cs

@@ -357,72 +357,4 @@ public IAsyncEnumerable<ChatCompletionResponse> StreamChatCompletionsRaw(
             cancellationToken
         );
     }
-
-    // Will be moved to a separate package.
-    internal async Task<byte[]> GenerateImageBytes(
-        string prompt,
-        string? user = null,
-        OpenAiImageSize size = OpenAiImageSize._1024,
-        CancellationToken cancellationToken = default)
-    {
-        if (string.IsNullOrWhiteSpace(prompt))
-            throw new ArgumentException("Value cannot be null or whitespace.", nameof(prompt));
-        var request = new ImageGenerationRequest(prompt, SizeToString(size), 1, "b64_json", user);
-        var response = await _httpClient.PostAsJsonAsync(
-            ImagesEndpoint,
-            request,
-            cancellationToken: cancellationToken
-        );
-        var responseContent = await response.Content.ReadAsStringAsync(cancellationToken);
-
-        if (!response.IsSuccessStatusCode)
-        {
-            throw new NotExpectedResponseException(response.StatusCode, responseContent);
-        }
-
-        var jsonResponse =
-            JsonSerializer.Deserialize<ImagesGenerationB64Response>(responseContent)!;
-        return Convert.FromBase64String(jsonResponse.Data[0].B64Json);
-    }
-
-    // Will be moved to a separate package.
-    internal async Task<Uri[]> GenerateImagesUris(
-        string prompt,
-        string? user = null,
-        OpenAiImageSize size = OpenAiImageSize._1024,
-        int count = 1,
-        CancellationToken cancellationToken = default)
-    {
-        if (string.IsNullOrWhiteSpace(prompt))
-            throw new ArgumentException("Value cannot be null or whitespace.", nameof(prompt));
-        if (count <= 0) throw new ArgumentOutOfRangeException(nameof(count));
-        var request = new ImageGenerationRequest(prompt, SizeToString(size), count, "url", user);
-        var response = await _httpClient.PostAsJsonAsync(
-            ImagesEndpoint,
-            request,
-            options: _nullIgnoreSerializerOptions,
-            cancellationToken: cancellationToken
-        );
-        var responseContent = await response.Content.ReadAsStringAsync(cancellationToken);
-
-        if (!response.IsSuccessStatusCode)
-        {
-            throw new NotExpectedResponseException(response.StatusCode, responseContent);
-        }
-
-        var jsonResponse =
-            JsonSerializer.Deserialize<ImagesGenerationUriResponse>(responseContent)!;
-        return jsonResponse.Data.Select(it => it.Url).ToArray();
-    }
-
-    private static string SizeToString(OpenAiImageSize size)
-    {
-        return size switch
-        {
-            OpenAiImageSize._256 => "256x256",
-            OpenAiImageSize._512 => "512x512",
-            OpenAiImageSize._1024 => "1024x1024",
-            _ => throw new ArgumentOutOfRangeException(nameof(size), size, null)
-        };
-    }
 }