[Bug]: write_source_files does not copy file permissions

### What happened?

write_source_files does not copy files with their permissions

### Version

Development (host) and target OS/architectures:

Output of `bazel --version`:

Version of the Aspect rules, or other relevant rules from your
`WORKSPACE` or `MODULE.bazel` file:

Language(s) and/or frameworks involved:

### How to reproduce

```shell
Create an executable file with `touch cmd.sh && chmod +x cmd.sh` and
copy the file with write_source_files and check if file
is still executable `([ -x ./.apko/range.sh ] && echo "executable") || echo "not executable"`
```

### Any other information?

_No response_

Start by locating the implementation of write_source_files and reproduce the issue with the provided shell commands: create cmd.sh, make it executable, and copy it. Done means the copied file remains executable and the reproduction check reports "executable".

Written by the indexing model from the issue text.