Generate explicit nested resource class methods

[richardm-stripe]

Summary

Replaces @nested_resource_class_methods decorator with explicit method definitions. This will make things easier to type.

To make this truly a no-op, we need to preserve the "helper" methods like stripe.Customer.balance_transactions_url and stripe.Customer.balance_transactions_request, even though we are no longer using them. Hence, we leave the @nested_resource_class_methods decorator in without any operations to provide these methods.

Testing

How can we be sure this doesn't change any behavior?

I have a little test script I added in Test nested resources that I ran both with and without the change.

git checkout richardm-explicit-nested-resource-class-methods-comparison
pip install -e .
python3 call_nested_resource_methods.py > /tmp/old
git checkout richardm-explicit-nested-resource-class-methods~1
pip install -e .
python3 call_nested_resource_methods.py > /tmp/new
sha256sum /tmp/old
# cb8e3ed1192dfe52df8d021e5a693ec55f0cca78d762f1a9bb75b87168a584ba  /tmp/old
sha256sum /tmp/new
# cb8e3ed1192dfe52df8d021e5a693ec55f0cca78d762f1a9bb75b87168a584ba  /tmp/new
wc -l /tmp/old
#     240 /tmp/old

(240 = 40 nested methods * 2 log statements * 3 test cases each)

This ~proves that, though there are a few differences in terms of whether the data is on the params dictionary or whether it is taken off via util.read_special_variable the behavior of everything is the same once it gets to api_requestor.