Decompiles WPL JSON to WPL-AI text format.
This enables round-trip transformation and allows LLMs to edit existing plans in the more readable WPL-AI format.
Example
iex> json = %{"plan" => %{"name" => "Test", "type" => "workout", ...}}
iex> {:ok, text} = Decompiler.decompile(json)
iex> text
"""
PLAN "Test"
TYPE workout
...
"""