MSM pre-computation

[DmytroTym]

Brief description

This PR adds pre-computation to the MSM, for some theory see this timecode of Niall Emmart's talk.
In terms of public APIs, one method is added. It does the pre-computation on-device leaving resulting data on-device as well. No extra structures are added, only precompute_factor from MSMConfig is now activated.

Performance

While performance gains are for now often limited by our inflexibility in choice of c (for example, very large MSMs get basically no speedup from pre-compute because currently c cannot be larger than 16), there's still a number of MSM sizes which get noticeable improvement:

Pre-computation factor	bn254 size 2^20 MSM, ms.	bn254 size 2^12 MSM, size 2^10 batch, ms.	bls12-381 size 2^20 MSM, ms.	bls12-381 size 2^12 MSM, size 2^10 batch, ms.
1	14.1	82.8	25.5	136.7
2	11.8	76.6	20.3	123.8
4	10.9	73.8	18.1	117.8
8	10.6	73.7	17.2	116.0

Here for example pre-computation factor = 4 means that alongside each original base point, we pre-compute and pass into the MSM 3 of its "shifted" versions. Pre-computation factor = 1 means no pre-computation. GPU used for benchmarks is a 3090Ti.

TODOs and open questions

• Golang APIs are missing;
• I mentioned that to utilise pre-compute to its full potential we need arbitrary choice of c. One issue with this is that pre-compute will become dependent on c. For now this is not the case as c can only be a power of 2 and powers of 2 can always share the same pre-computation. So apparently we need to make c a parameter of the precompute function to future-proof it from a breaking change. This is pretty unnatural and counterintuitive as c is typically chosen in runtime after pre-compute is done but I don't really see another way, pls let me know if you do. UPD: c is added into pre-compute function, for now it's unused and it's documented how it will change in the future.

Resolves #147
Co-authored with @ChickenLover

[DmytroTym]

This is ready for review although I plan to push another commit with more documentation of internals and public interfaces.