Add replace_methods argument to BatchLoader#batch

[smcgivern]

The existing cache argument does two things:

1. #__sync uses it to set a @synced instance variable, which tells
   later calls to #__sync not to reload the value when another method is
   called on it.
2. #__sync! uses it to replace methods on the proxied object with
   their 'real' equivalents.

This delegates responsibility for item 2 to the new replace_methods
argument instead. In testing (and in the benchmarks added here) we've
seen that #__replace_with! can actually take up an appreciable amount
of time, and removing it is faster, even though each individual method
call is slower.

The default for this new argument is to match cache. Only if it's
explicitly set to true or false will it not do that, and if it is
set to true and cache is false we raise an error, because that
doesn't make sense.

Closes #43.

[smcgivern]

@exAspArk would you mind taking a look, please?

[smcgivern]

Thanks @exAspArk, I made a few changes and added questions for the others.

[exAspArk]

@smcgivern thanks a lot! 🙌

[exAspArk]

I released your changes in v1.4.0 and added back your code (without raise) to avoid breaking changes 😸

batch-loader/lib/batch_loader.rb

Line 29 in 77d3264

@replace_methods = replace_methods.nil? ? cache : replace_methods

[smcgivern]

Thanks @exAspArk! ❤️

I like this explanation:

You may consider avoiding the "up front payment" and "pay as you go" with #method_missing by disabling the method replacement:

I'll look at getting this into GitLab this week.