Fix NameError in custom_attrs sample hook

[rootkiller6788]

Summary

The custom_attrs sample hook has referenced Tmpfile.new since it was added in 2017 (f4d6c28), but Tmpfile is not a constant Ruby defines anywhere — the stdlib tempfile class is Tempfile. As written, the hook crashes with

NameError: uninitialized constant CustomAttributes::Tmpfile

every time --custom-attr is passed on the command line, because pre_start runs Tmpfile.new('attributes') before the chef run starts.

This fixes the typo (Tmpfile → Tempfile) and adds the missing require 'tempfile' so the sample hook actually works out of the box.

Verification

• Tmpfile appears nowhere else in the repository and is not a Ruby stdlib class; Tempfile is the correct class (it is already used correctly in chefctl/src/spec/chefctl_spec.rb).
• All Tempfile methods used by the hook — new, write, close, path, unlink — are part of the Tempfile API.
• Reachable path: chefctl --custom-attr → CLI parsing sets @custom_attr → Chefctl::Plugin.get_plugin.pre_start → Tmpfile.new raises NameError.

Test plan

Static verification only; no Ruby runtime available locally. The change is a one-line constant rename plus a require.

[jaymzh]

This looks good, but it's still marked as a draft.

[rootkiller6788]

Thanks for the review! I’ll take this out of draft mode now so it can be merged.

[jaymzh]

@rootkiller6788 did you intentionally close this?