Use a dedicated flag for each tool in bench script (#818)
Taking some of Zanie's suggestions to make the custom-path API simpler
in the benchmark script. Each tool is now a dedicated argument, like:
```
python -m scripts.bench --pip-sync --poetry requirements.in
```
To provide custom binaries:
```
python -m scripts.bench \
--puffin-path ./target/release/puffin \
--puffin-path ./target/release/baseline \
requirements.in
```
