Zig arrays to be stack-allocated

[PDeveloper]

I have:

• [x] Read the project README, including the benchmark descriptions

Description of changes

To be closer to the C or Fortran versions, use stack-allocated arrays in the Zig version instead of dynamically heap-allocated arrays, providing more accurate results.

[gwenzek]

you should also remove the std.mem.eql at the top of levehenstein. C version isn't doing that. also I don't believe the benchmark is comparing eql strings anyway, so you're just doing more work without payout.

[D-Berg]

See this comment on why the arrays are heap allocated.

[zierf]

In order to be able to use arbitrary input sizes, stack-allocated arrays at comptime with fixed sizes are no longer an option.