Fix ctx.log type to accept any JSON-serializable type

[qianchongyang]

Problem

The ctx.info and similar logging methods have message: str type, but the MCP spec defines data: unknown to allow any JSON-serializable type. This inconsistency causes type errors when trying to log non-string data.

Solution

Updated type hints for logging methods to accept unknown instead of str:

• Changed message: str to message: unknown in ctx.info, ctx.debug, etc.
• Clarified extra parameter documentation
• Aligned with LoggingMessageNotificationParams and send_log_message signatures

Validation

# Now works without type error
ctx.info({"key": "value"})  # Dict logging
ctx.info([1, 2, 3])          # List logging
ctx.info(SomeObject())         # Object logging

Fixes #397