mini_racer-csim 0.21.1.5

A private fork of mini_racer (minimal embedded V8 for Ruby) adding browser-level behavior used by capybara-simulated: the V8 ES Module API, per-frame realms, realm reset, cross-process bytecode caching, an opt-in host namespace, and a batched module-graph loader with a URL module registry. These are niche browser-fidelity features; general users should use upstream mini_racer. It loads under its own `mini_racer_csim` require path and `MiniRacerCsim` namespace, so it never collides with upstream mini_racer in the same bundle.