docs: comprehensive investigation of issue #262 race condition

Add detailed documentation explaining the root cause of the MCP Client
Tool Call Hang bug, including:

- ASCII flow diagrams showing normal flow vs deadlock scenario
- Step-by-step timeline of the race condition
- Three confirmed reproduction methods with code examples
- Three confirmed fixes with explanations
- Explanation of why list_tools() works but call_tool() hangs
- References to all test files created

The root cause is zero-capacity memory streams combined with start_soon()
task scheduling, creating a race where send() blocks forever if receiver
tasks haven't started executing yet.

Github-Issue: #262

Author: claude