v0.1.5 — Concurrency & config fixes

v0.1.5 — Concurrency & config fixes

• Fixed: CompressRequest and BatchItem no longer hardcode gpt-4o-mini — model now falls back to config.default_model from .llmzip.config when not specified in the request
• Fixed: added threading.Lock with double-checked locking to resolver.py — prevents simultaneous LiteLLM fetches under concurrent batch load
• Fixed: _meta in fetcher and resolver now includes an explicit "source" field ("litellm" or "fallback") instead of inferring it from the note string
• Fixed: _fail() in loader.py now correctly typed as NoReturn
• Fixed: convert_bytes() in file_converter.py now closes the tempfile before passing it to MarkItDown, fixing PermissionError on Windows