Training

The main training interface:

let trainer := Trainer.new model
  { task := .regression
    optimizer := optim.adam { lr := 0.03 } }
let y0 ← trainer.predict x
let trained ← trainer.train data { steps := 200, batchSize := 16, logEvery := 25 }
trained.printSummary

The same interface supports regression, classification, custom losses, finite datasets, and streaming batches.