@spec backoff(pos_integer()) :: :ok

Sleeps for an exponentially increasing duration.

Formula: min(2s * 2^(attempt-1), 30s)

@spec max_attempts() :: pos_integer()

Returns the maximum number of retry attempts.

@spec with_retry(
  keyword(),
  (-> {:ok, map()} | {:error, term()})
) :: term()

Executes fun with retry on specified status codes.

fun must return the standard {:ok, response} | {:error, reason} tuple. The opts keyword list supports:

• :retriable_statuses — list of HTTP status codes to retry on (required)
• :on_success — fn response -> result for status 200 (required)
• :on_error — fn status, body -> result for non-retriable errors (required)
• :max_attempts — override default max attempts (optional)

On exhaustion, returns {:error, {:api_error, :max_retries_exceeded, last_status, last_body}} where last_status and last_body are from the final failed attempt.