fix: join the AP our scan picked without rescanning every channel

Every WiFi connect took about 17.6 s.  Our scan already picks the AP and
passes its BSSID and channel to WiFi.begin(), but the connect still ran
with WIFI_ALL_CHANNEL_SCAN.  So the driver swept every channel again
before it sent the first auth frame.  A capture of the join showed the AP
silent for 17.6 s, the radio on ch7 while the AP is on ch6, and then
auth, association and the handshake all done in 80 ms.

When the BSSID is known (the normal connect, the strongest-AP path and
roaming), use WIFI_FAST_SCAN: the driver starts on that channel and joins
the first match, and with bssid_set only that AP matches.  The hidden-SSID
path still uses the all-channel scan, since there it is what finds the
strongest AP (rstrouse/ESPSomfy-RTS#294).  Soft reboots now connect in
0.3-1.5 s.

Also log how long each join took and the AP's security mode, on the
connect line and on the roaming-scan lines, so a slow connect shows up.

One boot in the old logs connected in 2.47 s, and nothing in its log
explains it.  After a power cut the first attempts can still fail on the
AP side; a soft reboot sends a deauth first and doesn't have that problem.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Utils.h

@@ -74,6 +74,9 @@ struct RssiBroadcast {
 // connected it has to be at least minGain dBm stronger than the current AP so
 // a small swing doesn't make the device hop between APs.
 bool worthRoaming(bool connected, int currentRssi, int apRssi, int minGain);
+// A short name for a wifi_auth_mode_t value, for the logs.  The values up to
+// WAPI are the same in ESP-IDF 4.4 and 5.x.
+const char *wifiAuthModeName(uint8_t authMode);
 // Who gets a memStatus event.
 enum class heap_emit_t : uint8_t { none, client, broadcast, room };
 // num is the socket client asked for, 255 for everyone.  A broadcast goes out