This PR makes such changes:

1. Python’sdict objects are fairly heavy, even when empty. TheRequest object had a few of them. This PR makes their creation lazy (along with theflags list), so they are only created when they actually hold data. Previously, they were also created lazily, but once accessed, theRequest object would keep references to emptydicts/lists.In practice, these could just beNone instead. No, this breaks things. E.g.r.cookies[k]=v will return newly created empty dict, assignv tok key, and then discard this dict object since there is no references to it. Once accessed, they will be created and keeped. But when trying to assign empty dict or list to some ofRequest attributes, we won't store them.

2. Added__slots__ toRequest class and its subclasses

Before

Python3.13.3 (main,May222025,01:58:53) [MSCv.194364bit (AMD64)]onwin32>>>frompympler.asizeofimportasizeof>>>fromscrapyimportRequest>>>asizeof(Request("http://example.com"))1480>>>asizeof(Request("http://example.com"))1472>>>asizeof(Request("http://example.com"))>>> ...# internal python magic/interning of some objects???>>>asizeof(Request("http://example.com"))1368# final size

After

Python3.13.3 (main,May222025,01:58:53) [MSCv.194364bit (AMD64)]onwin32Type"help","copyright","credits"or"license"formoreinformation.>>>frompympler.asizeofimportasizeof>>>fromscrapyimportRequest>>>r=Request("http://example.com")>>>asizeof(r)432>>>r.cookies# sets empty dict{}>>>asizeof(r)496>>>r.cookies= {}# sets None>>>asizeof(r)432