Cool down before you install: give new gems a few days to be vetted

Bundler 4.0.13 introduces a cooldown feature that prevents automatic resolution to gem versions published within a specified timeframe, mitigating supply-chain attacks by allowing time for community scrutiny before installation. The opt-in mechanism refuses to resolve to a version until it has been public for at least N days, configurable per-source in the Gemfile or via global settings. Users can override the cooldown policy when security updates require immediate installation.