fix(nimble): Improve safety, fix bugs, and update docs across NimBLE examples

- Remove unused headers from examples
- Improve periodic adv/sync example functionality and readability
- Use ble_hs_id_infer_auto() instead of hardcoded BLE_OWN_ADDR_PUBLIC/RANDOM
- Add ble_hs_util_ensure_addr() calls in on_sync for proper address setup
- Use correct ext adv instance (0 instead of 1) in phy_prph, l2cap_coc, multi_conn
- Fix struct name: ble_gap_periodic_adv_enable_params -> ble_gap_periodic_adv_start_params
- Add CONFIG_BT_NIMBLE_GAP_SERVICE guards around ble_svc_gap_device_name_set
- Fix unsafe AD data parsing with bounds checks in central examples
- Fix UUID matching bugs (off-by-one loop condition and byte order) in
  phy_cent, htp_cent, and proximity_sensor_cent
- Fix ble_multi_conn_cent address type to use dynamic inference
- Remove contradictory sm_sc=0 after sm_sc=1 in ble_multi_adv
- Add CONFIG_BT_NIMBLE_EXT_ADV=y to ble_multi_adv sdkconfig defaults
- Check return values for ble_gap_set_host_feat, nimble_port_init
- Update tutorials and READMEs to match code changes

examples/bluetooth/nimble/bleprph/main/main.c

@@ -370,6 +370,8 @@ bleprph_gap_event(struct ble_gap_event *event, void *arg)
 
         if (event->passkey.params.action == BLE_SM_IOACT_DISP) {
             pkey.action = event->passkey.params.action;
+            /* WARNING: Hardcoded passkey for demonstration only.
+             * In production, generate a random passkey per pairing. */
             pkey.passkey = 123456; // This is the passkey to be entered on peer
             ESP_LOGI(tag, "Enter passkey %" PRIu32 "on the peer side", pkey.passkey);
             rc = ble_sm_inject_io(event->passkey.conn_handle, &pkey);
@@ -600,6 +602,8 @@ app_main(void)
 #endif
 
 #if MYNEWT_VAL(STATIC_PASSKEY) && NIMBLE_BLE_CONNECT
+    /* WARNING: Hardcoded passkey for demonstration only.
+     * In production, generate a random passkey per pairing. */
     ble_sm_configure_static_passkey(456789, true);
 #endif