Detect pyproject.toml changes and automatically run `poetry install` if needed

When using Stack (Haskell) and Cargo (Rust), if you manually add a new dependency in package.yaml or Cargo.toml respectively, then the next invocation of stack test or cargo test will detect the change and install the new dependency, whereas poetry run pytest could fail on the dependency missing. It would be great if Poetry could auto-detect the change instead of having to manually run poetry install again. Of course, for an individual user, it's easy to go through the poetry add interface instead, but it's more problematic when working on a team since other people won't immediately know after git pull whether there were updates requiring a poetry install.

Start by tracing the poetry run pytest command path and how Poetry reads pyproject.toml; the issue names no source files or tests. Define the change-detection behavior around dependency edits, then verify that a required poetry install occurs before execution without requiring users to run it manually.