compilers/1 and AshSandbox's `use Boundary` both keyed off the global
Mix.env(), which is the consuming app's env, not this package's own --
so the first real Hex consumer building in :dev/:test hit "module
Boundary is not loaded and could not be found" at lib/ash_sandbox.ex:130,
:boundary being only: [:dev, :test] scoped on this package's own deps
precisely so consumers never have to resolve it.

Gate both on Code.ensure_loaded?(Boundary). use Boundary also moves into
Code.eval_quoted/3: use inside a plain if still expands unconditionally
at compile time (confirmed on Elixir 1.20.2), so if alone does not defer
it and reintroduces the same failure.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>