fix: rename module to httpcache and fix tests location

Author: honzajavorek

src/apify/scrapy/extensions/cache.py renamed to src/apify/scrapy/extensions/httpcache.py

@@ -1,6 +1,6 @@
 from time import time
 
-from apify.scrapy.extensions.cache import from_gzip, read_gzip_time, to_gzip
+from apify.scrapy.extensions.httpcache import from_gzip, read_gzip_time, to_gzip
 
 FIXTURE_DICT = {'name': 'Alice'}