[HUF] Improve Huffman encoding speed

[HUF] Improve Huffman encoding speed

Improve Huffman encoding speed by 20% for gcc and 10% for clang.

| Compiler |     Benchmark     | Config  |   Dataset   | Ratio | Speed MB/s (dev) | Speed MB/s (huf-cspeed) | Speed MB/s (huf-cspeed - dev) |
|----------|-------------------|---------|-------------|-------|------------------|-------------------------|-------------------------------|
| gcc      | compress          | level_1 | enwik7      | 2.43  | 253.70           | 258.72                  | 2.0%                          |
| gcc      | compress          | level_1 | silesia     | 2.88  | 341.90           | 348.15                  | 1.8%                          |
| gcc      | compress_literals | level_1 | enwik7      | 1.49  | 761.83           | 912.76                  | 19.8%                         |
| gcc      | compress_literals | level_1 | silesia     | 1.28  | 754.83           | 902.37                  | 19.5%                         |
| gcc      | compress_literals | level_7 | enwik7      | 1.29  | 502.81           | 552.79                  | 9.9%                          |
| gcc      | compress_literals | level_7 | silesia     | 1.11  | 675.97           | 776.44                  | 14.9%                         |
| clang    | compress          | level_1 | enwik7      | 2.43  | 277.54           | 280.98                  | 1.2%                          |
| clang    | compress          | level_1 | silesia     | 2.88  | 369.98           | 375.46                  | 1.5%                          |
| clang    | compress_literals | level_1 | enwik7      | 1.49  | 828.83           | 918.41                  | 10.8%                         |
| clang    | compress_literals | level_1 | silesia     | 1.28  | 815.81           | 905.41                  | 11.0%                         |
| clang    | compress_literals | level_7 | enwik7      | 1.29  | 533.13           | 553.30                  | 3.8%                          |
| clang    | compress_literals | level_7 | silesia     | 1.11  | 714.52           | 775.38                  | 8.5%                          |