NumpyOps: add bound checks

[danieldk]

This PR adds various bounds checks to NumpyOps to prevent out-of-bound reads and writes:

• Check that which indices are in bounds for backprop_{maxout, reduce_max}.
• Check that dY and X shapes match in backprop for elementwise functions.
• Hook up ReLU to the PyTorch comparison tests.
• Check that lengths are valid in backprop_reduce_{mean, max, sum}.

[danieldk]

@explosion-bot please test_gpu

[explosion-bot]

🪁 Successfully triggered build on Buildkite

URL: https://buildkite.com/explosion-ai/thinc-gpu-test-suite/builds/34

[honnibal]

Nice! Love the advanced syntax for the nogil except. That's either relatively new, or I just never knew about it 🤯 . Either way, neat.