Update test file to be pypy compatible (and add requirements.txt)

[lgo]

• Swaps out the pympler memory grabber for resource which instead pulls total current resource usage. This is done because pympler's asizeof is not compatible with pypy.
• Adds in a gc.collect() call before the solution code. Along with the above change, this should ensure a solution's memory does not carry over -- assuming there are no memory leaks.
• Added a requirements.txt for the ease of just using pip install -r requirements.txt rather than fishing dependencies out while running it 😅

Here's what I've used to run this using pypy on MacOS.

# Install pypy3 and openblas (library)
brew install pypy3 openblas
# Update pypyp pip essentials.
pip_pypy3 install --upgrade pip setuptools wheel
# Compile numpy for pypy with the local openblas. without doing this,
# the pypy numpy installation will have runtime errors (at least on my setup)
OPENBLAS="$(brew --prefix openblas)" pip_pypy3 install numpy
# Install the other requirements.
pip_pypy3 install -r requirements.txt

# Vroom!
pypy3 tests/test_game.py

[lgo]

I'm also completely uncertain if this is the right thing, but was a suggested alternative for asizeof when I was googling around for the pypy error.

[zig1000]

Unfortunately I'm developing on windows which resource is not available on, and would like to keep it window-compatible, so I probably won't merge this. I assume pympler is the reason this isn't pypy-compatible, I'll try to look into some better memory measurer / one that's pypy-compatible when I have time.