fix: suppress urllib3 debug logging by default (closes #144)

[botbikamordehai2-sketch]

What

When a user configures their application's root logger at DEBUG level, they unexpectedly receive DEBUG messages from urllib3 (used internally by requests) such as:

DEBUG: Starting new HTTPS connection (1): api.kraken.com:443
DEBUG: https://api.kraken.com:443 "GET /0/public/Time HTTP/1.1" 200 None

These messages originate from urllib3's own logger and propagate to the root logger, cluttering application logs.

Fix

Set the urllib3 logger level to WARNING in the API.__init__ method so that internal HTTP connection details are suppressed by default. Users who want these messages can re-enable them by adjusting logging.getLogger('urllib3').setLevel(logging.DEBUG) in their own code.

Closes #144