Add #CALC! error type for Excel compatibility

[marcin-kordas-hoc]

Severity: Low (backlog)

HyperFormula's ErrorType enum does not include CALC. Excel uses #CALC! for several conditions:

• Zero dimensions in array functions (=SEQUENCE(0), =SEQUENCE(1,0))
• Empty array results
• Certain spill-related errors (separate from #SPILL!)

Currently these are mapped to ErrorType.NUM (#NUM!), which is the closest semantic match but diverges from Excel.

Known affected locations

• SequencePlugin.ts — zero dimension check returns #NUM! instead of #CALC!
• Potentially other array functions

Scope

Adding ErrorType.CALC would require:

• New enum value in src/Cell.ts
• New error message in src/error-message.ts
• Export handling in CellValueExporter
• Updates to functions currently returning #NUM! where #CALC! is correct
• Test updates

Impact

Cosmetic divergence from Excel. Does not affect functionality — formulas still error correctly, just with a different error type. Low priority unless Excel compatibility audit (2026 roadmap) prioritizes exact error type matching.

Found during SEQUENCE implementation (PR #1645).