Apply Compressed Sparse Row (CSR) compression to the parse table for
grammars that benefit, replacing the original dense + small split with
three flat arrays:
uint32_t parse_table_row_offsets[STATE_COUNT + 1]
uint16_t parse_table_columns[TOTAL_NNZ]
uint16_t parse_table_values[TOTAL_NNZ]
Heuristic for enabling CSR (per grammar, all three must hold):
1. LARGE_STATE_COUNT * SYMBOL_COUNT > STATE_COUNT * 40
Ensures the dense table is large enough relative to total state
count that savings outweigh the small-state grouping penalty.
2. dense table density < 45%
Ensures CSR actually saves space. Above ~50% density, CSR's
per-entry column indices cost more than the zeros they eliminate.
45% adds margin below the theoretical crossover.
3. LARGE_STATE_COUNT * SYMBOL_COUNT > 50,000
Avoids applying a format change to tiny grammars where fixed
overhead dominates.
Co-authored-by: Tuomas Hietanen <thorium@iki.fi>
