Support custom memory allocators in object slicer

[cthulhu-rider]

object slicer allocates byte buffers of certain size using Go built-in make function. From one side, it's normal default behavior for the library functionality. At the same time, some applications may desire to manage memory allocations deeper in order to improve app's performance

it's proposed to define app-level memory allocator (interface) and support it by the slicer as option. If set, this allocator is be used for processing, otherwise, slicer defaults to make

additionally, this approach will allow to get rid of

neofs-sdk-go/object/slicer/options.go

Lines 58 to 60 in 1db2fbf

	// SetPayloadBuffer sets pre-allocated payloadBuffer to be used to object uploading.
	// For better performance payloadBuffer length should be MaxObjectSize from NeoFS.
	func (x *Options) SetPayloadBuffer(payloadBuffer []byte) {

that requires buffer to be of size MaxObjectSize (64MB).

[roman-khimov]

Usually if you need a custom allocator you're doing something wrong, it'll be complicated and buggy. Pools/buffers should be sufficient for this.

[cthulhu-rider]

Pools/buffers should be sufficient for this

these are custom allocators to me