Add comprehensive documentation for per-session server instances

Co-authored-by: samanhappy <2755122+samanhappy@users.noreply.github.com>

tests/services/perSessionServers.test.ts

@@ -1,7 +1,6 @@
 import {
   getOrCreatePerSessionServer,
   cleanupPerSessionServers,
-  handleCallToolRequest,
 } from '../../src/services/mcpService';
 import { ServerConfig } from '../../src/types';