[httpx] replace searx.poolrequests by searx.network

settings.yml:

* outgoing.networks:
   * can contains network definition
   * propertiers: enable_http, verify, http2, max_connections, max_keepalive_connections,
     keepalive_expiry, local_addresses, support_ipv4, support_ipv6, proxies, max_redirects, retries
   * retries: 0 by default, number of times searx retries to send the HTTP request (using different IP & proxy each time)
   * local_addresses can be "192.168.0.1/24" (it supports IPv6)
   * support_ipv4 & support_ipv6: both True by default
     see https://github.com/searx/searx/pull/1034
* each engine can define a "network" section:
   * either a full network description
   * either reference an existing network

* all HTTP requests of engine use the same HTTP configuration (it was not the case before, see proxy configuration in master)

searx/search/checker/impl.py

@@ -13,7 +13,7 @@ from langdetect import detect_langs
 from langdetect.lang_detect_exception import LangDetectException
 import httpx
 
-from searx import poolrequests, logger
+from searx import network, logger
 from searx.results import ResultContainer
 from searx.search.models import SearchQuery, EngineRef
 from searx.search.processors import EngineProcessor
@@ -75,8 +75,8 @@ def _is_url_image(image_url):
     while retry > 0:
         a = time()
         try:
-            poolrequests.set_timeout_for_thread(10.0, time())
-            r = poolrequests.get(image_url, timeout=10.0, allow_redirects=True, headers={
+            network.set_timeout_for_thread(10.0, time())
+            r = network.get(image_url, timeout=10.0, allow_redirects=True, headers={
                 'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0',
                 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
                 'Accept-Language': 'en-US;q=0.5,en;q=0.3',