Make Windows rustc builds work with response files

Windows Once builds of large Rust graphs no longer hit the OS command line length limit (os error 206). The full post-rustc argument list is routed through a rustc response file on Windows for both build script and crate compiles. Response files are written verbatim from the declared arguments, cmd_args(..., use_arg_file=...) now lives in the graph action layer instead of each prelude, the executor materializes declared argument files before the action runs, and an explicit scratch_dir keeps helper files separate from durable target outputs. Other hosts keep their inline argument paths.