Cover all functionality with basic unit tests

[eyalroz]

Most code in the library is currently not covered by any unit tests. Let's add that coverage.

• [x] src/kat/containers/span.hpp
• [x] src/kat/containers/array.hpp
• [x] src/kat/containers/tuple.hpp
• [x] src/kat/on_device/time.cuh
• [x] src/kat/on_device/c_standard_library/string.cuh
• [x] src/kat/on_device/miscellany.cuh
• [x] src/kat/on_device/wrappers/atomics.cuh
• [x] src/kat/on_device/wrappers/builtins.cuh
• [x] src/kat/on_device/wrappers/shuffle.cuh
• [x] src/kat/on_device/shared_memory/operations.cuh
• [x] src/kat/on_device/shared_memory/basic.cuh
• [x] src/kat/on_device/non-builtins.cuh
• [x] src/kat/on_device/constexpr_math.cuh
• [x] src/kat/on_device/math.cuh
• [x] src/kat/on_device/collaboration/warp.cuh
• [x] src/kat/on_device/collaboration/grid.cuh
• [x] src/kat/on_device/collaboration/block.cuh
• [x] src/kat/on_device/sequence_ops/warp.cuh
• [x] src/kat/on_device/sequence_ops/grid.cuh
• [x] src/kat/on_device/sequence_ops/block.cuh
• [x] src/kat/on_device/streams/*
• [ ] src/kat/on_device/ranges.cuh

Skipping:

• src/kat/on_device/unaligned.cuh <- Dropped from the repository (but expected to make a comeback soon - with unit tests)
• src/kat/on_device/grid_info.cuh <- These are all one-liners; it's like testing an int add(int x, int y) { return x+y; } function - what can you test about it?
• src/kat/on_device/printing.cuh <- Dropped from the repository (for now)
• src/kat/on_device/ptx/* <- Mostly covered by "builtins" unit tests, and not quite "user-facing".

[eyalroz]

This should have been closed, and now reopened for ranges...