SSE: Add support for SSE handler options (#503)

[IAmSurajBobade]

mcp/sse: add support to provide for options for SSE transport

• Add SSEOptions struct to define SSE handler options.
• Update Signature of NewSSEHandler to accept SSEOptions
• Ensure Logger is never nill, using ensureLogger helper method
• update unit tests
• update example tests

Fixes #503

[jba]

The SSEOptions work has to be separate from the logging.
We want the options in today, but the logging can wait another day or two.
Please send a separate PR.

[jba]

Refer to #507.

[IAmSurajBobade]

closing as duplicate of #508