Use tempfile for Eldritch Tests

[Cictrone]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

adds tmp files for our eldritch tests so we dont need to hassle with removing files/platform dependencies

Which issue(s) this PR fixes:

n/a

Test Output:

root ➜ .../realm/cmd/implants/eldritch (tmp_file_fix ✗) $ cargo test
   Compiling eldritch v0.1.0 (/workspaces/realm/cmd/implants/eldritch)
    Finished test [unoptimized + debuginfo] target(s) in 4.71s
     Running unittests (/workspaces/realm/cmd/implants/target/debug/deps/eldritch-909020e101a46f5d)

running 9 tests
test file::exists_impl::tests::test_exists_dir ... ok
test file::append_impl::tests::test_append_existing ... ok
test file::exists_impl::tests::test_exists_no_dir ... ok
test file::append_impl::tests::test_append_nonexisting ... ok
test file::exists_impl::tests::test_exists_file ... ok
test file::hash_impl::tests::test_hash ... ok
test file::exists_impl::tests::test_exists_no_file ... ok
test file::copy_impl::tests::test_copy ... ok
test tests::test_library_bindings ... ok

[KCarretto]

Nice!