Use function factory pattern to pass cutting functions to `sim_gs_n()`

[jdblischak]

Follow-up to #195. Closes #196.

This PR makes the following updates:

• Instead of passing a list of quoted get_analysis_date() expressions that then need to be evaluated, the argument cutting of sim_gs_n() now accepts a list of cutting functions. These functions are created by the function factory create_cutting()
• Instead of passing quoted test functions to the argument test of sim_gs_n(), only the test function itself is passed, and any further arguments are passed to the testing function via ...
• Various other code improvements

Note that I didn't fully convert maxcombo(). I don't think I fully understand the purpose of this function. Its arguments are quoted functions, but they are never evaluated. Instead their arguments for rho and gamma are extracted and passed to fh_weight(). Is there any reason that maxcombo() couldn't instead just receive the vectors of rho and gamma directly? And why is maxcombo() needed when fh_weight() already exists?

[LittleBeannie]

Thanks for applying the function factory, @jdblischak ! Before the merge, could you please introduce us to the changes and new syntax tomorrow?

[nanxstats]

Overall looking good. Let's try follow the testing best practices in designing your test suite:

• Avoid the library(gsDesign2) call and qualify namespaces explicitly.
• Move the logic at top of the test file with "test file scope" into a function within a "helper" file and call the function to setup things at the start of individual tests.

[jdblischak]

Before the merge, could you please introduce us to the changes and new syntax tomorrow?

@LittleBeannie Yes, of course. I'll explain everything in today's meeting. Also note that this morning I also converted the maxcombo() interface to accept vectors instead of quoted function expressions.

[jdblischak]

Overall looking good. Let's try follow the testing best practices in designing your test suite:

@nanxstats I switched to gsDesign2:: and created helper functions defined in a separate helper file. Please let me know if you'd like me to make any further modifications.