Default logging level `INFO` is too verbose and hard to change

[MarketDataDev03]

Title: Default logging level INFO is too verbose and hard to change

Problem

By default the SDK logs every client initialization (3+ INFO lines) and every HTTP request at INFO level,
which floods the terminal. Lowering the level requires knowing about the MARKETDATA_LOGGING_LEVEL env var —
not discoverable from the public API.

Reproduction

from marketdata import MarketDataClient
c = MarketDataClient(token="...")
# 2026-05-26 16:22:34 - marketdata.logger - INFO - Initializing MarketDataClient
# 2026-05-26 16:22:34 - marketdata.logger - INFO - Base URL: https://api.marketdata.app
# 2026-05-26 16:22:34 - marketdata.logger - INFO - API Version: v1
# ...one INFO line per request after that

Suggested fix

1. Lower the default level to WARNING (src/marketdata/settings.py:27).
2. Move the init-time Base URL / API Version messages to DEBUG (src/marketdata/client.py:46-47) —
   useful for debugging, noise otherwise.