Batch convert commitments/proofs to bytes

[jtraglia]

In compute_cells_and_kzg_proofs, converting proofs to bytes in batch is 3.44% faster with precompute=8.

Before:

$ go clean -cache && GOMAXPROCS=1 go test -test.bench=Benchmark/ComputeCellsAndKZGProofs -test.run=^$ ./bindings/go 
goos: darwin
goarch: arm64
pkg: github.com/ethereum/c-kzg-4844/v2/bindings/go
cpu: Apple M1
Benchmark/ComputeCellsAndKZGProofs(precompute=0)                       4         263398458 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=1)                       2         908959958 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=2)                       3         488505694 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=3)                       3         350817750 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=4)                       4         277039625 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=5)                       5         240792967 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=6)                       5         213914367 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=7)                       6         198406333 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=8)                       6         184162486 ns/op
Benchmark/ComputeCellsAndKZGProofsParallel(count=8)                    4         289445594 ns/op
PASS
ok      github.com/ethereum/c-kzg-4844/v2/bindings/go   96.002s

After:

$ go clean -cache && GOMAXPROCS=1 go test -test.bench=Benchmark/ComputeCellsAndKZGProofs -test.run=^$ ./bindings/go
goos: darwin
goarch: arm64
pkg: github.com/ethereum/c-kzg-4844/v2/bindings/go
cpu: Apple M1
Benchmark/ComputeCellsAndKZGProofs(precompute=0)                       4         260788177 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=1)                       2         901798042 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=2)                       3         479930694 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=3)                       3         344812153 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=4)                       4         274845333 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=5)                       5         237340850 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=6)                       5         210313592 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=7)                       6         193029160 ns/op
Benchmark/ComputeCellsAndKZGProofs(precompute=8)                       6         177826458 ns/op
Benchmark/ComputeCellsAndKZGProofsParallel(count=8)                    4         268851688 ns/op
PASS
ok      github.com/ethereum/c-kzg-4844/v2/bindings/go   93.767s

[b-wagn]

LGTM!

[kevaundray]

LGTM.

I wonder if we can do the same in recover_cells_and_kzg_proofs

[jtraglia]

I wonder if we can do the same in recover_cells_and_kzg_proofs

@kevaundray Ah I was too focused on speeding up compute_cells_and_kzg_proofs. Yes, we can do this (batch conversions) in two other places. I've just pushed two commits for this, please re-review.

[kevaundray]

LGTM ser