fix(core): preserve large stat u64 fields

[NathanFlurry]

• Preserves exact large filesystem stat u64 fields from the sidecar protocol as decimal shadow fields while keeping default stat fields JSON-safe numbers.
• Wires Node-style { bigint: true } stat options through sync, callback, promise, and file-handle stat paths.
• Adds regression coverage for generated stat values above Number.MAX_SAFE_INTEGER so large host device IDs no longer crash during adapter conversion.

Validation:

• pnpm --dir packages/core exec vitest run tests/state.test.ts
• pnpm --dir packages/core check-types
• pnpm --dir packages/browser check-types
• pnpm --dir packages/build-tools check-types
• pnpm --dir packages/build-tools exec node scripts/build-v8-bridge.mjs

[railway-app]

🚅 Environment secure-exec-pr-273 in rivet-frontend has no services deployed.

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🚅 Deployed to the secure-exec-pr-273 environment in secure-exec

Service	Status	Web	Updated (UTC)
secure-exec	😴 Sleeping (View Logs)	Web	Jul 4, 2026 at 8:37 pm