Add streamable http support

[shahar4499]

🚀 Add Streamable HTTP Transport Support

This PR adds support for Streamable HTTP transport as the new primary transport method.
#61

⚠️ Breaking Changes

• mount() method is now deprecated and will be removed in a future version
• New explicit methods:
  • mount_http() - Recommended for HTTP transport (new default)
  • mount_sse() - For SSE transport (backwards compatibility)
• For backwards compatibility, the old mount() method defaults to SSE transport with a deprecation warning

🛠 More Fixes

• Input Validation: Leverage the SDK's input validation to catch input errors BEFORE they reach the FastAPI server
• Session management: Leverage the SDK's MCP session management capabilities for both HTTP and SSE
• Request Context: Leverage the SDK's capability to forward request_context to use the HTTP request information (such as auth) in tool handlers.
• Security: Built-in support for transport security settings and proper session validation

[codecov]

Codecov Report

❌ Patch coverage is 84.87395% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
fastapi_mcp/transport/http.py	78.57%	15 Missing ⚠️
fastapi_mcp/server.py	93.33%	3 Missing ⚠️

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