Increased model support, test isolation, bug fixes

• added support for Anthropic, Bedrock and Ollama models, using litellm;
• added --prompt-family to select between prompt styles/versions;
• separated prompts into more easily modifiable module;
• implemented test collection isolation and changed to using it by default;
• various improvements to "bad test" finder;
• various adjustments to the prompts;
• implemented asynchronous test running and coverage collection;
• various bug fixes;
• improved packaging, so that project description shows properly on PyPI;