Remove blocking config portal mode and refactor API

- Remove setConfigPortalBlocking() API and _configPortalIsBlocking member variable
- Remove blocking while(1) loop from startConfigPortal()
- Change startConfigPortal() return type from boolean to void
- Change stopConfigPortal() return type from bool to void
- Make stopConfigPortal() immediately shutdown portal (call shutdownConfigPortal() directly)
- Remove unused portalAbortResult and portalTimeoutResult variables
- Update all comments to remove blocking mode references
- Simplify debug messages (remove 'non-blocking' references)
- Update tests to remove setConfigPortalBlocking() calls
- All 43 tests passing

The config portal is now always non-blocking, requiring users to call
process() periodically in their main loop. This aligns with the async
web server architecture and simplifies the API.

test/test_wifimanager/tests/test_static_ip.cpp

@@ -16,8 +16,6 @@ void test_set_ap_static_ip_config() {
     // Set AP static IP
     wm.setAPStaticIPConfig(ip, gw, sn);
     
-    // Use non-blocking mode
-    wm.setConfigPortalBlocking(false);
     wm.setConfigPortalTimeout(10);
     
     // Start portal and verify IP is actually set
@@ -72,11 +70,8 @@ void test_ap_static_ip_application() {
     
     wm.setAPStaticIPConfig(customIP, customGW, customSN);
     
-    // Use non-blocking mode
-    wm.setConfigPortalBlocking(false);
     wm.setConfigPortalTimeout(10);
     
-    // Note: In non-blocking mode, startConfigPortal() returns false even when successful
     wm.startConfigPortal("TestAP");
     TEST_ASSERT_TRUE(wm.getConfigPortalActive());