feat(run): allow custom strategy and state

labgrid_config_toolchain now accepts a state attribute, which becomes available to binaries executed by labgrid_genrule and labgrid_run_binary as the LG_STATE env var. This matches the same name as labgrid-client expects, to make it convenient to call the CLI from the binary directly. This state will be used to transition the strategy specified in the Labgrid config file.

We've cleaned up how arguments are passed from the toolchains to the executor as part of this change. It now uses an args file instead of custom env vars.