replace deprecated Buffer apis with new API

[sidorares]

Ref: #380

Buffer(number) and new Buffer(number) replaced with Buffer.unsafeAlloc(number)
new Buffer(string) and new Buffer(array) replaced with Buffer.from

some new Buffer() still left in tools and benchmarks

[sidorares]

@sushantdhiman would you be able to review?

[sushantdhiman]

We are using allocUnsafe a lot (I guess for performance), its good but we need to be sure those buffer are completely filled.

[sidorares]

yes, everywhere it's used the intention is to fill all bytes of buffer. There is one exception, in handshake packet there is 10 bytes zero filler so I'm using Buffer.alloc(size, 0) + packet.skip(10) there (instead of filling 10 bytes manually). I'll try to double check again myself. I wander maybe we could use some version of Buffer in tests that allows to check that there is no uninitialised space in resulting buffers.

[sushantdhiman]

It appears most of time unsafeAlloc is used to build packets or headers that are filled to the end. So it LGTM.

We might be able to add unit tests for each Header/Packet type and try initialize them with mock data, at the end we could inspect if Header/Packet was properly prepared and fully filled. But that will be a big test suite to add, we should add it in separate PR(s)

[sidorares]

Yes agree ( in general, having unit tests for all packets would be good)