Add bounded-memory spilling to SCC aggregation

Normalized profile

What this task asks for

Add an opt-in bounded-memory mode that spills per-file aggregation results to disk without changing output. --bounded-memory-max-in-memory-files <int> (required when enabled, must be > 0). Spilling must occur whenever enforcing --bounded-memory-max-in-memory-files would otherwise be violated (e.g., max=1 with many files => spills>0 when stats are enabled). For json, json2, csv, and csv-stream, output content must be byte-for-byte identical to the unbounded --format-multi output. For csv-stream specifically, bounded-memory mode must honor file destinations when specified (e.g., csv-stream:/tmp/out.csv writes the same csv-stream bytes that would have gone to stdout into that file). If using --format-multi, the ordering/concatenation of the combined output must remain identical to current behavior. When sorting is requested, csv-stream must emit rows in that sorted order.