Enhance FastMCP server with port override functionality

[yeoyujie]

Motivation and Context

Previously, the port could only be set during the initialization of the server. By allowing the port to be passed directly to run(), developers can now override the listening port at runtime. This change aligns with the ergonomics of popular Python web frameworks, enhancing the developer experience.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• [] I have added appropriate error handling
• I have added or updated documentation as needed

[ihrpr]

Thank you for the contribution!

The port can already be modified at runtime before calling run():

  mcp = FastMCP("My Server")
  mcp.settings.port = 9000  # not a very nice way, but it works
  mcp.run(transport="sse")

The Settings class is mutable (not frozen). Thile adding it as a parameter is a cleaner approach, it adds complexity and might lead to the confusion which parameter to use.