this MR
- adds `criterion` as a dependency
- creates a new `benches/recoding.rs` benchmark file
- makes the following `pub`lic
  - `fec::combine`
  - `field` and `field::split_data_into_field_elements`

## example results
| bytes   | shards | k  | mean (us) |
| ------- | ------ | -- | --------- |
| 1       | 2      | 2  | 0.127     |
| 1       | 2      | 4  | 0.179     |
| 1       | 2      | 8  | 0.283     |
| 1       | 2      | 16 | 0.504     |
| 1       | 4      | 2  | 0.346     |
| 1       | 4      | 4  | 0.506     |
| 1       | 4      | 8  | 0.823     |
| 1       | 4      | 16 | 1.451     |
| 1       | 8      | 2  | 0.789     |
| 1       | 8      | 4  | 1.155     |
| 1       | 8      | 8  | 1.89      |
| 1       | 8      | 16 | 3.383     |
| 1       | 16     | 2  | 1.669     |
| 1       | 16     | 4  | 2.478     |
| 1       | 16     | 8  | 4.023     |
| 1       | 16     | 16 | 7.147     |
| 1024    | 2      | 2  | 1.02      |
| 1024    | 2      | 4  | 1.076     |
| 1024    | 2      | 8  | 1.172     |
| 1024    | 2      | 16 | 1.395     |
| 1024    | 4      | 2  | 2.981     |
| 1024    | 4      | 4  | 3.15      |
| 1024    | 4      | 8  | 3.453     |
| 1024    | 4      | 16 | 4.089     |
| 1024    | 8      | 2  | 6.907     |
| 1024    | 8      | 4  | 7.244     |
| 1024    | 8      | 8  | 7.969     |
| 1024    | 8      | 16 | 9.452     |
| 1024    | 16     | 2  | 15.169    |
| 1024    | 16     | 4  | 16.14     |
| 1024    | 16     | 8  | 17.086    |
| 1024    | 16     | 16 | 20.266    |
| 1048576 | 2      | 2  | 1470.966  |
| 1048576 | 2      | 4  | 1097.899  |
| 1048576 | 2      | 8  | 1091.298  |
| 1048576 | 2      | 16 | 1091.544  |
| 1048576 | 4      | 2  | 3274.852  |
| 1048576 | 4      | 4  | 3272.68   |
| 1048576 | 4      | 8  | 3251.877  |
| 1048576 | 4      | 16 | 3272.872  |
| 1048576 | 8      | 2  | 7582.074  |
| 1048576 | 8      | 4  | 7599.012  |
| 1048576 | 8      | 8  | 7584.59   |
| 1048576 | 8      | 16 | 7569.575  |
| 1048576 | 16     | 2  | 16274.986 |
| 1048576 | 16     | 4  | 16303.905 |
| 1048576 | 16     | 8  | 16313.429 |
| 1048576 | 16     | 16 | 16310.305 |