Function load_file 

pub async fn load_file(
    kb: &dyn KnowledgeBase,
    scope: &TenantScope,
    path: &Path,
    config: &ChunkConfig,
) -> Result<usize, Error>

Load a single file and index its chunks into the knowledge base under the given tenant.

SECURITY (F-KB-3): bounded by KNOWLEDGE_LOAD_FILE_MAX_BYTES.