fix: Prevent StdioTransport premature disconnection (Variant 3: stream_set_blocking)

[ArtemYurov]

Problem:

• MCP server disconnects after ~60 seconds of inactivity
• fread() blocks and returns false when no data available
• This triggers "Failed to read from STDIN" error and breaks the listening loop

Solution (Variant 3):

• Explicitly set stream_set_blocking(true) for STDIN
• Keep feof() check for EOF detection
• Simplest code among all variants

Testing:
✅ Tested for 150+ seconds without disconnections
✅ Compatible with macOS and other UNIX systems
✅ Simplest implementation

Changes:

• Added stream_set_blocking($this->input, true) before the listening loop
• Keep while (!\feof($this->input) && !$this->closing) condition
• Fixed $deferred->resolve() to pass null argument (line 129)

Limitations:
❌ Graceful shutdown does not work properly
❌ Cannot check $this->closing flag during fread() blocking ❌ Server will not exit until data arrives on STDIN ❌ Not recommended for production use due to shutdown issues

Comparison to other variants:

• Simplest code but sacrifices graceful shutdown capability
• Use Variant 1 (stream_select + feof) for production instead