fix: prevent StreamWriter from disposing HttpResponse.Body in ConfigurableResponseNegotiator

[Copilot]

StreamWriter constructed directly over HttpResponse.Body disposes the underlying response stream when the writer is disposed, which can corrupt the ASP.NET Core response pipeline.

Change

Added leaveOpen: true to the StreamWriter constructor, with bufferSize: -1 to preserve the default buffer size:

// Before
await using var textWriter = new StreamWriter(res.Body, encoding);

// After
await using var textWriter = new StreamWriter(res.Body, encoding, bufferSize: -1, leaveOpen: true);

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[Copilot]

Pull request overview

Prevents ConfigurableResponseNegotiator from accidentally closing HttpResponse.Body by ensuring the StreamWriter does not dispose the underlying response stream, avoiding corruption of the ASP.NET Core response pipeline.

Changes:

• Construct StreamWriter with leaveOpen: true when writing to HttpResponse.Body.

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