fix(lib): give each thread its own VCDiffDecoder - #1240

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5, actions/setup-java@17f84c3641ba7b8f6deff6309fc4c864478f5d62, gradle/actions/setup-gradle@d9c87d481d55275bb5441eef3fe0e46805f9ef70. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/