update the API (dragoon/komodo!71)

## changelog
- rename the `encode` function to `prove` and have it take _shards_ instead of an _encoding matrix_: this is to isolate the "encoding" process inside the `fec` module and leave the main `komodo::prove` only compute the "proof", i.e. the commits of the data

from
```rust
fn encode<F, G, P>(
    bytes: &[u8],
    encoding_mat: &Matrix<F>,
    powers: &Powers<F, G>,
) -> Result<Vec<Block<F, G>>, KomodoError>
```
to
```rust
fn prove<F, G, P>(
    bytes: &[u8],
    powers: &Powers<F, G>,
    k: usize,
) -> Result<Vec<Commitment<F, G>>, KomodoError>
```
- rename `fec::Shard.combine` to `fec::Shard.recode_with` to get rid of "combine"
- rename `fec::recode` to `fec::recode_with_coeffs` to show that this version takes a list of coefficients
- rename `Block.commit` to `Block.proof`: "commit" should be "commits" and it's usually refered to as "proof"
- split `prove` further into `prove` and `build`: `prove` now outputs a `Vec<Commitment<F>>`, `build` simply takes a `Vec<Shard<F>>` and a `Vec<Commitment<F>>` and outputs a `Vec<Block<F>>`
- add `fec::recode_random` that does the "shard" part of `recode` to wrap around `fec::recode_with_coeffs`
- remove `R: RngCore` from the signature of `zk::setup`, to avoid having to pass a generic `_` annotation everywhere `zk::setup` is used, same change has been applied to `recode` and the `generate_random_powers` in `main.rs`

from
```rust
fn setup<R: RngCore, F: PrimeField, G: CurveGroup<ScalarField = F>>(
    max_degree: usize,
    rng: &mut R,
) -> Result<Powers<F, G>, KomodoError> {
```
to
```rust
fn setup<F: PrimeField, G: CurveGroup<ScalarField = F>>(
    max_degree: usize,
    rng: &mut impl RngCore,
) -> Result<Powers<F, G>, KomodoError> {
```

### some extra minor changes
- remove some useles generic type annotations, e.g. `prove::<F, G, P>` can become a simpler `prove` most of the time, i.e. when there is at least one generic annotation somewhere in the scope