fix(objectql): apply a formula field's declared scale where the value is produced

.changeset/formula-scale-at-producer.md

@@ -0,0 +1,29 @@
+---
+"@objectstack/objectql": patch
+---
+
+Apply a `formula` field's declared `scale` when the formula is evaluated
+(#10280). `Field.formula({ scale: 2 })` was accepted and then ignored: a
+percentage formula such as `(record.num_responses * 100.0) / record.num_sent`
+**returned** `41.666666666666664`, so the API response — and the record page
+rendered from it — carried all fifteen digits despite the declaration.
+
+The value is now rounded where it is produced, in the engine's formula
+evaluation, so all three surfaces that materialize a formula inherit it: list
+reads, single-record reads, and the record a write responds with.
+
+- **Rounding is `Number(v.toFixed(scale))`** — round-half-away-from-zero, the
+ same arithmetic the console's client-side computed columns use. Negatives
+ round away from zero: `-1.5` at `scale: 0` is `-2`, not `-1`.
+- **A formula declaring no `scale` is unchanged** and keeps full precision.
+- **Non-numeric results are untouched** — a formula returning a string,
+ boolean or `null` is returned as-is.
+- A formula value is **returned, never stored** — it is virtual and has no
+ column. Rounding it at the producer is what makes an app's own copy of that
+ result writable into a stored `DECIMAL(10, 2)`-style field, which previously
+ failed that field's decimal validation.
+
+Unchanged: `scale` on a **caller-supplied** number (`Field.number`,
+`Field.currency`, …) is still enforced by **rejection** (`max_scale`), never by
+rounding. A value someone sent has an author to refuse; a platform-computed
+formula result does not.