Low: BuildExecutor.cacheFile captures workDir path once at construction rather than using getter dynamically

[harsharajkumar]

In buildExecutor.js:124 inside the constructor, this.cacheFile is set to path.join(this.workDir, '.build-cache.json'), evaluating the workDir getter only once at startup. If getProofdeskDataRoot() were to return a different path after construction (e.g. due to env var changes), the cache file path would be stale. All other uses of this.workDir call the getter dynamically, making cacheFile an inconsistency.