[BUG] Proxy doesn't change when using different username

[MrDebugger]

Describe the bug:
The curl_cffi library does not switch proxies correctly when only the username in the proxy URL changes, while other components (host, port, and password) remain the same. This issue is observed when multiple proxies are used sequentially in a single session, resulting in all requests incorrectly using the first proxy's credentials.

To Reproduce:
Steps to reproduce the behavior:

Set up a Session with proxies that differ only in the username.
Execute requests to a target website (e.g., httpbin.org/ip) that returns the requester's IP.
Notice that the session fails to update the proxy after the initial set, using the first proxy for all requests.

from curl_cffi.requests import Session

proxies = {
    'Proxy1': 'http://username1:password@host:port',
    'Proxy2': 'http://username2:password@host:port',
}

s = Session()

for proxy_key, proxy_url in proxies.items():
    s.proxies = {
        'http': proxy_url,
        'https': proxy_url,
    }
    r = s.get('https://httpbin.org/ip')
    print(proxy_key, r.json())

Expected behavior:
Each request should reflect the IP of the corresponding proxy defined by its username. However, the actual output shows the IP of the first proxy for both requests, indicating that the proxy change was not recognized.

Versions:
OS: Ubuntu 20.04.4 LTS
curl_cffi version: 0.6.3
Python version: 3.10.12

Additional context:
The session used is synchronous.
The proxy credentials issue suggests a possible mishandling in the proxy management within the session, particularly with caching or parsing mechanisms.

[perklet]

I'm afraid this is how libcurl works. See my comments here.

#210 (comment)

You can try adding Connection: close header or downgrading to HTTP/1.1, but it's not guaranteed to work.

IMHO, this is the correct behavior actually. Establishing new connection to the same address is quite inefficient, and these auto-rotating proxies abuse the behavior.