perf: og-inline-fetch-assets blocks Vite transform pipeline with sync I/O

[Divkix]

Problem

The vinext:og-inline-fetch-assets plugin (packages/vinext/src/index.ts) uses synchronous fs.readFileSync() in Vite's transform hook at two locations. This blocks the Vite transform pipeline during builds, especially when multiple modules reference the same font/asset files.

Expected behavior

The transform hook should use async fs.promises.readFile() and cache repeated reads to avoid redundant disk I/O.

Fix

PR #435