Run All Terraform Binary Ignored

terraform_binary respected by run --all when both tofu and terraform are on PATH

run --all ignored a unit's terraform_binary setting and fell back to the auto-detected default (OpenTofu when both binaries are on PATH). The per-unit options used to execute each unit are cloned from the stack options, whose binary path is the auto-detected default, and the configured value was never applied to them.

Each unit now honors its own terraform_binary, matching the behavior of a single run. Setting --tf-path or TG_TF_PATH still takes precedence over the config value.