perf: more elegant solution to mem dump using unsafe and generics

[gbotrel]

• refactor: expose pedersen basis slices
• feat: more elegant solution to mem dump using unsafe and generics

Motivation; enable other gnark objects (like groth16.ProvingKey) to be written and read very fast (though not portable). Limit code duplication between curves, fields, proof systems, etc.

• Adds utils/unsafe with WriteSlice[S ~[]E, E any](w io.Writer, s S) error ... ;
• kzg.UnsafeToBytes(...) []byte is now WriteDump(w io.Writer) error

🔥 Benchmarks for kzg SRS dump 🔥 --> (I mean using unsafe is a cheat, we just benchmark the non-unsafe method + real IO)

benchmark                                      old ns/op      new ns/op      delta
BenchmarkSerializeSRS/WriteTo-10               1227334792     1200767042     -2.16%
BenchmarkSerializeSRS/WriteRawTo-10            1291239625     1275224792     -1.24%
BenchmarkSerializeSRS/UnsafeToBytes-10         288414938      49002102       -83.01%
BenchmarkDeserializeSRS/UnsafeReadFrom-10      1589721583     1607936042     +1.15%
BenchmarkDeserializeSRS/UnsafeFromBytes-10     283540219      81233306       -71.35%

benchmark                                      old allocs     new allocs     delta
BenchmarkSerializeSRS/WriteTo-10               540            540            +0.00%
BenchmarkSerializeSRS/WriteRawTo-10            542            541            -0.18%
BenchmarkSerializeSRS/UnsafeToBytes-10         522            512            -1.92%
BenchmarkDeserializeSRS/UnsafeReadFrom-10      1046           1047           +0.10%
BenchmarkDeserializeSRS/UnsafeFromBytes-10     1029           1031           +0.19%

benchmark                                      old bytes      new bytes      delta
BenchmarkSerializeSRS/WriteTo-10               2147544696     2147544696     +0.00%
BenchmarkSerializeSRS/WriteRawTo-10            4295028640     4295028632     -0.00%
BenchmarkSerializeSRS/UnsafeToBytes-10         1610821246     67176202       -95.83%
BenchmarkDeserializeSRS/UnsafeReadFrom-10      1627598752     1627598848     +0.00%
BenchmarkDeserializeSRS/UnsafeFromBytes-10     1610820720     1610820744     +0.00%

[github-actions]

📦 github.com/consensys/gnark-crypto/kzg

kzg/kzg.go:40:10: cannot use &kzg_bn254.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bn254/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bn254/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:42:10: cannot use &kzg_bls12377.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bls12-377/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bls12-377/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:44:10: cannot use &kzg_bls12378.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bls12-378/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bls12-378/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:46:10: cannot use &kzg_bls12381.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bls12-381/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bls12-381/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:48:10: cannot use &kzg_bls24315.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bls24-315/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bls24-315/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:50:10: cannot use &kzg_bls24317.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bls24-317/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bls24-317/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:52:10: cannot use &kzg_bw6761.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bw6-761/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bw6-761/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:54:10: cannot use &kzg_bw6633.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bw6-633/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bw6-633/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)
kzg/kzg.go:56:10: cannot use &kzg_bw6756.SRS{} (value of type *"github.com/consensys/gnark-crypto/ecc/bw6-756/kzg".SRS) as SRS value in return statement: *"github.com/consensys/gnark-crypto/ecc/bw6-756/kzg".SRS does not implement SRS (missing method UnsafeFromBytes)

[ivokub]

LGTM. Imo we can add a simple guard in case the slice to write is empty to have better errors, but I think normally shouldn't happen.

[ivokub]

Add guard in case len(s) == 0.