Improve content type detection from responses

[kzu]

And also default format to Uri if not provided via request options.

The file extension > mime-type mapping makes this somewhat future-proof if the service ever starts returning non-jpeg format.

We'd need to update the library to provide the desired format anyway since there isn't a way currently of doing so.

[kzu]

🧪 Details on Ubuntu 24.04.3 LTS

❌ xAI.Tests.SanityChecks.IntegrationTest

Grpc.Core.RpcException : Status(StatusCode="Internal", Detail="internal server error")
   at xAI.GrokChatClient.GetResponseAsync(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken) in /_/src/xAI/GrokChatClient.cs:line 40
   at Microsoft.Extensions.AI.FunctionInvokingChatClient.GetResponseAsync(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)
   at xAI.Tests.SanityChecks.IntegrationTest() in /_/src/xAI.Tests/SanityChecks.cs:line 167

❌ xAI.Tests.SanityChecks.IntegrationTestStreaming

Grpc.Core.RpcException : Status(StatusCode="Internal", Detail="internal server error")
   at Grpc.Net.Client.Internal.HttpContentClientStreamReader`2.MoveNextCore(CancellationToken cancellationToken)
   at Grpc.Core.AsyncStreamReaderExtensions.ReadAllAsyncCore[[T]](IAsyncStreamReader`1 streamReader, CancellationToken cancellationToken)+MoveNext()
   at Grpc.Core.AsyncStreamReaderExtensions.ReadAllAsyncCore[[T]](IAsyncStreamReader`1 streamReader, CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()
   at xAI.GrokChatClient.<GetStreamingResponseAsync>g__CompleteChatStreamingCore|8_0(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+MoveNext() in /_/src/xAI/GrokChatClient.cs:line 68
   at xAI.GrokChatClient.<GetStreamingResponseAsync>g__CompleteChatStreamingCore|8_0(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+MoveNext() in /_/src/xAI/GrokChatClient.cs:line 68
   at xAI.GrokChatClient.<GetStreamingResponseAsync>g__CompleteChatStreamingCore|8_0(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()
   at Microsoft.Extensions.AI.FunctionInvokingChatClient.GetStreamingResponseAsync(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+MoveNext()
   at Microsoft.Extensions.AI.FunctionInvokingChatClient.GetStreamingResponseAsync(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+MoveNext()
   at Microsoft.Extensions.AI.FunctionInvokingChatClient.GetStreamingResponseAsync(IEnumerable`1 messages, ChatOptions options, CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()
   at System.Linq.AsyncEnumerable.<ToListAsync>g__Impl|188_0[[TSource]](ConfiguredCancelableAsyncEnumerable`1 source)
   at System.Linq.AsyncEnumerable.<ToListAsync>g__Impl|188_0[[TSource]](ConfiguredCancelableAsyncEnumerable`1 source)
   at xAI.Tests.SanityChecks.IntegrationTestStreaming() in /_/src/xAI.Tests/SanityChecks.cs:line 177

🧪 Details on Ubuntu 24.04.3 LTS

from retest v1.1.0 on .NET 10.0.1 with 💜 by @devlooped