v0.2.10 — per-file process isolation by default

Changed

• libuild test runs each test file in its own process (per-file isolation, now the default). Previously every file was bundled into one process per platform. For runtimes that don't return native/off-heap memory to the OS mid-process (bun/JSC), a large jsdom-backed suite grew until it thrashed and never finished; node (V8) reclaimed and passed the same bundle. Each file now bundles and runs in its own process (reusing the setup-file injection and externalization), so native memory is freed between files; independent files run in parallel bounded to ~cpus-1. Results aggregate across files into the per-platform summary, and per-file lines report as each finishes. No flag — this is just how the runner works. Browser keeps its single-page Playwright execution. Resolves #16.