VirusTotal Client factory should trust_env

[erichutchins]

Attempting to use the GTI MCP from behind a proxy and I had to modify server/gti/gti_mcp/server.py to trust the environment variables.

def _vt_client_factory(unused_ctx) -> vt.Client:
  api_key = os.getenv("VT_APIKEY")
  if not api_key:
    raise ValueError("VT_APIKEY environment variable is required")
  return vt.Client(api_key, trust_env=True)  # explicitly set trust_env to inherit HTTPS_PROXY

https://virustotal.github.io/vt-py/api/client.html

trust_env (bool) – Get proxies information from HTTP_PROXY/
HTTPS_PROXY environment variables if the parameter is True (False 
by default).