docs(cart-shopify): add @example to mockShopifyTransport

[filiphsps]

Summary

Addresses reviewer blocker on merged PR #1965: mockShopifyTransport is Tier-1 (via the ./testing sub-path export) and requires an @example.

Verification

• typecheck
• lint
• rebased on origin/master
• JSDoc-only diff
• changeset added

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	82.35% (🎯 65%)	5528 / 6712
🔵	Statements	81.1% (🎯 60%)	6107 / 7530
🔵	Functions	81.53% (🎯 75%)	1523 / 1868
🔵	Branches	66.82% (🎯 50%)	3580 / 5357

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
packages/cart/shopify/src/testing.ts	62.72%	60%	85%	67.02%	106-111, 150, 151, 152, 153, 154, 155, 162, 203, 209, 236-241, 244, 282-321

Generated in workflow #12873 for commit eed0cb0 by the Vitest Coverage Report Action

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.27%. Comparing base (e806f66) to head (eed0cb0).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1970   +/-   ##
=======================================
  Coverage   81.27%   81.27%           
=======================================
  Files         453      453           
  Lines        8427     8427           
  Branches     2693     2693           
=======================================
  Hits         6849     6849           
  Misses       1578     1578           

Components	Coverage Δ
App: Storefront	79.28% <ø> (ø)
App: Admin	90.05% <ø> (ø)
App: Landing	∅ <ø> (∅)
Pkg: @nordcom/commerce-db	93.91% <ø> (ø)
Pkg: @nordcom/commerce-errors	100.00% <ø> (ø)
Pkg: @nordcom/commerce-marketing-common	∅ <ø> (∅)
Pkg: @nordcom/commerce-shopify-graphql	100.00% <ø> (ø)
Pkg: @nordcom/commerce-shopify-html	94.93% <ø> (ø)
Layer: Apps	80.84% <ø> (ø)
Layer: Packages	81.74% <ø> (ø)

Flag	Coverage Δ
unit	81.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/cart/shopify/src/testing.ts	66.37% <ø> (ø)