Serialize small Ints as JSON Ints

[antonydellavecchia]

Serialize Integers between 1 - 2^53 and 2^53 -1 as JSON numbers.

possible this wont need upgrade, but will see what tests say.

[antonydellavecchia]

handles part of #5482
or rather deals with the main issue but doesn't address the uni variate polynomials comment in the issue.
but arguably should resolve it?

[benlorenz]

Did you do any tests how this affects size and loading / savingspeed for any of the very large files that we have?

[antonydellavecchia]

this branch timings/allocations and filesize

julia> surface = load(joinpath(Oscar.oscardir, "data/Surfaces/k3_d12_pi14.mrdi"));

julia> @time save("/tmp/bla", surface)
  0.004963 seconds (90.13 k allocations: 3.246 MiB)

julia> @time load("/tmp/bla");
  0.059450 seconds (112.93 k allocations: 7.121 MiB)

julia> filesize("/tmp/bla")
78385

current master timings timings/allocations and filesize

julia> @time save("/tmp/bla", surface)
  0.007207 seconds (133.33 k allocations: 4.399 MiB)

julia> @time load("/tmp/bla");
  0.059776 seconds (130.93 k allocations: 7.516 MiB)

julia> filesize("/tmp/bla")
114385