Individual recovery exercise
@type sides() :: :both | :left | :right
@type t() :: %WplAi.AST.RecoveryExercise{ body_part: String.t() | nil, hold_seconds: integer(), intensity_rpe: integer() | nil, modality: String.t() | nil, name: String.t(), pnf: WplAi.AST.PnfSpec.t() | nil, reps: integer(), sides: sides() | nil }