Feature/memory range dimension

[swmal]

Performance: Virtual InMemoryRange for full column references

Formulas using full column references (e.g. $A:$A, B:B) in dynamic array expressions caused severe performance degradation. EPPlus materialized 1,048,576 rows regardless of actual data, resulting in millions of unnecessary allocations and iterations.

Changes

Virtual InMemoryRange — New concept separating physical size (backed by data) from logical size (full column). A _virtualDefaultValue field stores the pre-computed result for empty rows, avoiding per-cell allocation. Operators (+, *, =, &, etc.) compute the default once and propagate it through the chain.

MATCH/XlookupScanner — GetMaxItemsRow now uses GetAddressDimensionAdjusted to limit search to physical rows instead of iterating 1M rows.

FormulaRangeAddress.HasFormulas — Loop clamped to worksheet dimension, eliminating 1M iterations per SUMIFS/AVERAGEIFS call with full column references.

Key files

• InMemoryRange.cs — Virtual rows, default value propagation
• RangeOperationsOperator.cs — SetVirtualDefault, SetVirtualDefaultForRanges
• RangeHelper.cs — GetPhysicalRows
• XlookupScanner.cs — Bounded search
• FormulaRangeAddress.cs — Bounded HasFormulas

Result

Benchmark workbook: 10.8 minutes → 2.6 seconds (~250x improvement). Full test suite (6200+ tests) green.