Fix macOS SSE server test connection issues

[0xeb]

Problem

The fastmcpp_sse_server test was failing on macOS CI (both Debug and Release) with connection errors:

• "Connection handling canceled (7)"
• "POST request failed"
• "SSE GET request failed: Failed to read connection (4)"

Tests passed on Ubuntu and Ubuntu ARM but consistently failed on macOS.

Root Cause

The test had a "connection readiness check" (lines 51-67) that:

1. Immediately canceled the connection (line 61 returned false)
2. On macOS, this left the server in a bad state for subsequent connections
3. The POST and SSE connections then failed due to lingering connection issues

Solution

1. Removed problematic connection test - The immediate-cancel test was causing more harm than good on macOS
2. Increased server startup wait - From 1s to 2s to ensure server is fully ready
3. Added delay before SSE connection - 100ms grace period before the SSE thread attempts connection

Testing

• Local build and test (Windows)
• Waiting for macOS CI results
• Ubuntu CI should still pass

Impact

• Test now waits slightly longer (1s additional delay) but is more reliable across platforms
• No functional changes to the SSE server implementation
• Removes flaky connection check that was macOS-specific issue