- fixed `encoding.rs/decode_coeff_i64` for the case `k < basek2`
- `glwe/external_product.rs/external_product_scratch_space` did not allocate enough space for [`a_dft`](829b8be610/core/src/glwe/external_product.rs (L83)) when `k_out < k_ggsw`. Fixed by replacing `in_size` with `ggsw_size`.
- `glwe/ops.rs/add` sets `basek` and `k`of `self` GLWECiphertext whic is invalid because the `size` which depends on `inner` data remains unchanged.
- (not a fix) expose `backend` from `core`.
