Pure-Python helper that resolves a fusion.report's line_specs against
account_totals -> ordered list of report row dicts. Supports three spec
types: account_type_prefix (sum accounts by type), account_id (single
account, drill-downable), and compute='subtotal' (sum last N rows).
Comparison-period support: variance_pct computed automatically when
comparison_totals are supplied.
5 new tests, 32 total passing.
Made-with: Cursor
