feat: switch from num-bigint-dig to crypto-bigint´

The biggest refactor (to date)

Replaces all usage of `num-bigint-dig` based `BigInt` usage with the new
`crypto-bigint` crate, using `BoxedUint`


Current known issue is that we do have a performance regression, which
will be able to get rid of over time:

```
# crypto-bigint

# macbook m1
test bench_rsa_2048_pkcsv1_decrypt      ... bench:   7,184,387.50 ns/iter (+/- 425,598.69)
test bench_rsa_2048_pkcsv1_sign_blinded ... bench:  13,453,579.10 ns/iter (+/- 686,276.31)

# AMD
test bench_rsa_2048_pkcsv1_decrypt      ... bench:   9,260,832.80 ns/iter (+/- 30,013.38)
test bench_rsa_2048_pkcsv1_sign_blinded ... bench:  16,610,079.40 ns/iter (+/- 251,292.53)

# master

# macbook m1
test bench_rsa_2048_pkcsv1_decrypt      ... bench:   1,117,479.15 ns/iter (+/- 31,334.30)
test bench_rsa_2048_pkcsv1_sign_blinded ... bench:   1,337,437.55 ns/iter (+/- 88,624.39)

# AMD
test bench_rsa_2048_pkcsv1_decrypt      ... bench:   1,414,348.80 ns/iter (+/- 12,585.71)
test bench_rsa_2048_pkcsv1_sign_blinded ... bench:   1,685,650.00 ns/iter (+/- 11,105.71)
```

## TODOs

- [x] switch internal storage for `RsaPrivateKey`
- [x] switch internal storage for `RsaPublicKey`
- [x] switch all code to use the new `decrypt` implementation
- [x] update public traits using `BigUint` to return owned versions
- [x] fix blinding implementation
- [x] switch decryption algorithm with precompute to use crypto-bigint
ops
- [x] go through other algorithms and update what can be done without
having primality checks implemented
- [x] review & update code for constant time operation
- [x] review & update code for performance
- [x] benchmarks

---------

Co-authored-by: Fethbita <[email protected]>

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.81.0 # MSRV
+          - 1.83.0 # MSRV
           - stable
         target:
           - thumbv7em-none-eabi
@@ -35,7 +35,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.81.0 # MSRV
+          - 1.83.0 # MSRV
           - stable
     steps:
       - uses: actions/checkout@v4
@@ -44,7 +44,7 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
       - uses: RustCrypto/actions/cargo-hack-install@master
-      - run: cargo hack test --release --feature-powerset --exclude-features nightly,getrandom,serde
+      - run: cargo hack test --release --feature-powerset --exclude-features getrandom,serde
       - run: cargo test --release --features getrandom
       - run: cargo test --release --features serde
 
@@ -66,5 +66,4 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: nightly-2024-10-06
-      - run: cargo test --release --features nightly
       - run: cargo build --benches

.github/workflows/workspace.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: RustCrypto/actions/cargo-cache@master
       - uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: 1.81.0
+          toolchain: 1.83.0
           components: clippy
       - run: cargo clippy --all -- -D warnings
 
@@ -40,7 +40,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           # We need Nightly for doc_auto_cfg
-          toolchain: nightly-2024-06-25
+          toolchain: nightly-2024-11-30
       - uses: Swatinem/rust-cache@v2
       - env:
           RUSTDOCFLAGS: "-Dwarnings --cfg docsrs"