fix: process Walmart in-store receipt charges

[eshaffer321]

What changed

• fall back to the receipt total when a completed Walmart IN_STORE order has exactly one CREDITCARD payment and its ledger is empty
• preserve payment-pending behavior for online, split-tender, gift-card, and non-positive-total orders
• document the root cause and live verification

Root cause

Walmart returns complete payment metadata and totals for in-store receipts on the order payload, but its separate order-ledger endpoint returns no payment methods. Itemize treated every empty ledger as an uncharged order, so completed in-store purchases were skipped indefinitely.

Validation

• regression test proved the pre-fix payment-pending failure and now passes
• go test ./... -race
• golangci-lint and go vet ./...
• live dry-run against all three affected receipts matched $9.88, $32.10, and $10.69 Monarch transactions and finished Processed=3 Skipped=0 Errors=0
• dry-run made no Monarch writes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.89%. Comparing base (b01acb1) to head (5eb422b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #73      +/-   ##
==========================================
+ Coverage   61.81%   61.89%   +0.08%     
==========================================
  Files          46       46              
  Lines        6021     6034      +13     
==========================================
+ Hits         3722     3735      +13     
  Misses       2046     2046              
  Partials      253      253              

Flag	Coverage Δ
unittests	61.89% <100.00%> (+0.08%)	⬆️

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

Files with missing lines	Coverage Δ
internal/adapters/providers/walmart/order.go	72.54% <100.00%> (+2.54%)	⬆️

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