fix: match Walmart aggregate ledger charges

[eshaffer321]

Summary

• Fall back to matching multi-delivery Walmart orders by their total final ledger charges.
• Consolidate exact aggregate transaction subsets when Monarch posts charges in a different grouping.
• Deduplicate repeated Walmart purchase-history summaries before fetching details.
• Prefer exact subset totals over tolerated one-cent near-matches.

Verification

• go test ./...
• go test ./... -race
• Pre-commit formatting, golangci-lint, and go vet ./...
• Live isolated dry-runs for Walmart orders 200015335172701 and 200015072601480
• Targeted production syncs completed successfully: the first applied 2 splits; the second consolidated $75.60 + $0.01 to $75.61 and applied 3 splits.

No -force was used.

[codecov]

Codecov Report

❌ Patch coverage is 84.53608% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.23%. Comparing base (b986777) to head (52d1b72).

Files with missing lines	Patch %	Lines
internal/application/sync/handlers/walmart.go	86.66%	4 Missing and 4 partials ⚠️
internal/adapters/providers/walmart/provider.go	61.11%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   60.53%   61.23%   +0.69%     
==========================================
  Files          46       46              
  Lines        5757     5837      +80     
==========================================
+ Hits         3485     3574      +89     
+ Misses       2042     2027      -15     
- Partials      230      236       +6     

Flag	Coverage Δ
unittests	61.23% <84.53%> (+0.69%)	⬆️

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

Files with missing lines	Coverage Δ
internal/domain/matcher/subset.go	58.82% <100.00%> (+58.82%)	⬆️
internal/adapters/providers/walmart/provider.go	33.66% <61.11%> (+6.28%)	⬆️
internal/application/sync/handlers/walmart.go	61.33% <86.66%> (+5.59%)	⬆️

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