Add minimal SSE response support to azure-core

[Xiaofei Cao (XiaofeiCao)]

Description

Adds minimal Server-Sent Events support to azure-core RestProxy responses.

• Preserves text/event-stream response bodies as non-replayable BinaryData instead of buffering an unbounded stream.
• Detects streaming intent from the request Accept header or response Content-Type header.
• Couples async and sync Response<BinaryData> body termination to the underlying HttpResponse, closing it on completion, error, or cancellation.
• Avoids buffering or logging SSE response bodies in HttpLoggingPolicy.
• Adds focused coverage for media-type detection, logging behavior, replayability, and response ownership.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes. N/A: internal azure-core RestProxy behavior; no package-level public API was added.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up your commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

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