fix: make timeUnitBandPosition work with timeUnit on color

[fandu-db]

The problem

Chart's color is broken when timeUnitBandPosition and a temporal color are used together

Minimum repro:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "data/stocks.csv"},
  "mark": {"type": "bar"},
  "encoding": {
    "x": {"field": "symbol", "type": "nominal"},
    "y": {"aggregate": "mean", "field": "price", "type": "quantitative"},
    "color": {"timeUnit": "year", "field": "date"}
  },
  "config": {"bar": {"timeUnitBandPosition": 0}}
}

Root cause

We are checking isRectWithOffset inconsistently
In data/aggregate.ts
isRectBasedMark(mark) && bandPosition !== 0.5 && isXorY(channel)

In scale/domain.ts
isRectBasedMark(mark) && bandPosition !== 0.5

That leads to the Vega spec trying to access a derived field that does not exist

Solution in this PR:
Added the missing && isXorY(channel) to domain.ts

AFTER