OLMIS-8244: Add packs-to-order preview hint

[michaldev0]

OLMIS-8244 — "Will be ordered as X pack(s)" preview hint

https://openlmis.atlassian.net/browse/OLMIS-8244

Companion to the backend fix OpenLMIS/openlmis-fulfillment#55,
which converts requisition-less order quantities from doses to packs at send. Because the entered
doses are rounded to whole packs on send, the user should see the result beforehand.

Change

openlmis-quantity-unit-input now renders a hint under the quantity input — e.g.
"Will be ordered as 2 pack(s) (168 doses)" — in both Doses and Packs input modes.

• quantity-unit.service.js — adds packsToOrder(quantity, netContent, packRoundingThreshold, roundToZero), a JS port behaviourally identical to the backend OrderableDto.packsToOrder /
  canonical referencedata Orderable#packsToOrder, so the preview matches what the backend stores.
• openlmis-quantity-unit-input.jsx — showPacksToOrderHint prop + memoised hint; hidden when
  netContent === 1 (nothing to round) or quantity is empty/zero.
• New message key openlmisInputDosesPacks.willBeOrderedAsPacks and a small style for the hint.

Tests

• quantity-unit.service.spec.js (new) — 7 cases mirroring the backend OrderableDtoTest
  one-for-one (exact, round-up, round-down within threshold, sub-pack min-1, roundToZero, zero net
  content, non-positive quantity).

E2E verified (live)

Hint correct across exact (252→3), round-up (130→2), round-down (100→1, 200→2, 90→1), sub-pack
min-1 (20→1); Packs mode (2 packs + 50 doses → 3); hidden for netContent=1 (Male Condom) and for
quantity 0/empty.

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud