Parallelize RegistryToolLoader initialization for faster startup

[g2vinay]

Resolves #1026

perf: Parallelize RegistryToolLoader initialization to reduce startup time

This change addresses a ~20 second startup delay when running the Azure MCP
Server in VS Code via the VSIX extension.

Problem:
The RegistryToolLoader was sequentially initializing 47 MCP server processes
(one for each Azure service command group). With each server taking ~400-500ms
to start, the cumulative delay was 20+ seconds.

Change:

• Parallelized server initialization using Task.WhenAll()
• All servers now initialize concurrently instead of sequentially
• Added comprehensive diagnostic logging with timing metrics

Performance Improvement:

• Before: ~20,000ms (sequential initialization)
• After: ~1,500-2,000ms (parallel initialization)
• Speedup: 10-15x faster

The diagnostic logs now show:

• Number of servers discovered
• Success/failure counts
• Total tools loaded
• Precise initialization time