Rebalancing & delay

Composable, strictly causal (T, N) transforms between an allocator/signal and backtest: the effective book drifts with asset returns and trading is throttled on a calendar (rebalance_calendar), inside a no-trade band (rebalance_band) or under a per-bar turnover budget (rebalance_turnover_cap), plus whole-lot discretization (discretize) and an execution delay (delay).

rebalance_calendar(W, X[, every])	Rebalance to target weights on a fixed calendar, drift between.
rebalance_band(W, X[, band, mode])	Rebalance only when the drift leaves a no-trade band around the target.
rebalance_turnover_cap(W, X[, budget])	Move toward the target each bar under a per-bar turnover budget.
discretize(W, prices[, capital, lot, ...])	Round a target weight book to whole lots on a fixed capital base.
delay(W[, steps])	Shift a weight book forward by a fixed number of bars.