bootstrap: report missing pyproject.toml nicely
build_harness requires pyproject.toml to be present before build-harness install
can be used.
$ build-harness install
Unexpected error. Check log for details.
Traceback (most recent call last):
File ".venv/lib/python3.8/site-packages/build_harness/commands/bootstrap.py", line 314, in install
project_dependencies = acquire_project_dependencies(command_state.project_path)
File ".venv/lib/python3.8/site-packages/build_harness/_project.py", line 76, in acquire_project_dependencies
toml_data = _acquire_pyprojecttoml_data(project_dir)
File ".venv/lib/python3.8/site-packages/build_harness/_project.py", line 48, in _acquire_pyprojecttoml_data
return toml_data
UnboundLocalError: local variable 'toml_data' referenced before assignment
Fix the assignment error and report the failure nicely to user.