Configurable HTTP timeouts and connection limit for cache transfers

The CLI’s shared HTTP client now reads HTTP timeouts and the per-host connection limit from environment variables, so self-hosted operators on constrained or proxied network paths can tune them without recompiling. The new knobs are TUIST_HTTP_TIMEOUT_INTERVAL_FOR_RESOURCE (default 90s), TUIST_HTTP_TIMEOUT_INTERVAL_FOR_REQUEST (default 120s), and TUIST_HTTP_MAXIMUM_CONNECTIONS_PER_HOST (default 20). The previous hardcoded 90s resource timeout caused cache downloads to fall back to a source build once a single artifact stalled at the proxy; raising this timeout lets a slow-but-recoverable download finish as a cache hit. Existing behavior is unchanged when these variables are unset.