[Core] UTF-8 byte 기반 HeuristicTokenEstimator 구현 - #58

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-java@v4, gradle/actions/setup-gradle@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Failed to restore gradle-home-v1|Linux|build[49fcb02b4545b42262c489efa6c9a32d]-63c25875b7dbfd88235a5f05554016f70dffab27: Error: Cache service responded with 400