fix(django): finish streaming spans on response close

[ahmadalguydi]

What does this PR do?

Fixes #4681 by keeping Django server spans active for StreamingHttpResponse objects until Django invokes the response's guaranteed close() lifecycle hook.

The existing response status/header instrumentation and response hook still run in process_response; duration metrics, active-request accounting, context detachment, and span finalization are deferred only for streaming responses. The close wrapper is idempotent and finalizes telemetry even when the original close method raises.

Checklist

• Added regression coverage for deferred span completion and idempotent close handling.
• Ran the Django middleware test suite.
• Ran git diff --check and Python compilation.

Test result: 42 passed for instrumentation/opentelemetry-instrumentation-django/tests/test_middleware.py.