Enhance Ollama model management and performance tuning

- Updated the `provision_llm` function to utilize the `/api/tags` endpoint for verifying available models, improving accuracy in model management.
- Introduced a new `already_have_ollama_tag` function to ensure exact tag matching, preventing mismatches during model checks.
- Enhanced the `pull_stream` function to require a successful status from the API before proceeding, ensuring reliable model downloads.
- Added logic to handle unwritten blob files, improving the robustness of the model pulling process.
- Updated documentation and tests to reflect these changes, ensuring clarity and reliability in Ollama model operations.

src/gpu_rent/llm_runtime.py

@@ -127,6 +127,17 @@ def parse_ollama_models(path: Path) -> list[OllamaModelEntry]:
     return out
 
 
+def already_have_ollama_tag(have: set[str], wanted: str) -> bool:
+    """Exact tag match only — qwen2.5:3b must not satisfy qwen2.5:7b."""
+    if wanted in have:
+        return True
+    if ":" not in wanted and f"{wanted}:latest" in have:
+        return True
+    if wanted.endswith(":latest") and wanted.rsplit(":", 1)[0] in have:
+        return True
+    return False
+
+
 def write_ollama_models_preset(path: Path, preset: str) -> None:
     key = (preset or "recommended").strip().lower()
     if key not in OLLAMA_PRESETS: