Fix TCP connection spike: disable HTTP keep-alive and add request timeouts on cached sessions

[Copilot]

Every cached requests.Session holds a urllib3 connection pool (pool_connections=10, pool_maxsize=10 by default) of idle open TCP sockets. With a 30-minute cache TTL, connections accumulate under load until the OS exhausts file descriptors — system freezes. After TTL expiry the cleanup thread closes all sessions and releases sockets — system auto-recovers. Matches the described symptom exactly.

Changes

bit_login/login.py

• Connection: close header on all sessions — urllib3 closes the TCP socket immediately after each response instead of returning it to the idle pool. Eliminates idle socket accumulation in cached sessions.
• _TimeoutHTTPAdapter — thin HTTPAdapter subclass that injects a 30-second default timeout via kwargs.setdefault. Prevents hung connections from accumulating without modifying any call site. Mounted as separate instances for http:// and https://.

class _TimeoutHTTPAdapter(HTTPAdapter):
    def __init__(self, *args, **kwargs):
        self._default_timeout = kwargs.pop('timeout', 30)
        super().__init__(*args, **kwargs)

    def send(self, request, **kwargs):
        kwargs.setdefault('timeout', self._default_timeout)
        return super().send(request, **kwargs)

bit_login/config.py

• Changed Connection: keep-alive → Connection: close in the base headers dict for consistency.

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