Decodes one CASCADE encoding unit into an owned F3.Column.

The default implementation is F3.Decoder.Native. Tests replace it by setting Application.put_env(:f3, :decoder, module). The module must implement this behaviour. F3.read/2 uses that module for every unit and does not call it when the native build is absent.

Examples

A test double returns one owned column and does not touch a file:

defmodule SampleDecoder do
  @behaviour F3.Decoder

  @impl true
  def decode(_bytes, :uncompressed, :i64) do
    F3.Column.from_native(:i64, 1, <<1::little-64>>, nil)
  end

  def decode(_bytes, _compression, _type) do
    {:error, F3.Error.unsupported_encoding(:decode, "unsupported unit")}
  end
end

decode/3 receives the unit bytes, the compression atom, and the physical type atom. It returns {:ok, column} or {:error, %F3.Error{}}. It should not raise for a unit it refuses.