[Task] Investigate `bls12_381_plus` dependency type incompatibility

## Description
The 0.8.16 version of [bls12_381_plus](https://crates.io/crates/bls12_381_plus/0.8.16) introduces changes to type conversion that may break builds due to conflicting implementations of From trait.

```
error[E0119]: conflicting implementations of trait `From` for type `Issuer`
--> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/identity_credential-1.3.0/src/credential/issuer.rs:43:1
|
43 | / impl From for Issuer
44 | | where
45 | | T: Into,
| |_______________^
|
= note: conflicting implementation in crate `bls12_381_plus`:
- impl From for ::BigInt;
Pinning this dependency to the previous version hotfixes build issues when used as an indirect dependency here (via [zkryptium](https://crates.io/crates/zkryptium)).
```

Version should be able to opened up in the future. Pin implemented in #1278

## Change checklist
Add an `x` to the boxes that are relevant to your changes, and delete any items that are not.

- [ ] The feature or fix is implemented in Rust and across all bindings whereas possible.
- [ ] The feature or fix has sufficient testing coverage
- [ ] All tests and examples build and run locally as expected
- [ ] Every piece of code has been document according to the documentation guidelines.
- [ ] If conceptual documentation (mdbook) and examples highlighting the feature exist, they are properly updated.
- [ ] If the feature is not currently documented, a documentation task Issue has been opened to address this.