variadic higher order functions

[bbbales2]

Description

This is an issue for making variadic forms of the other higher order functions (similar to #1642)

• integrate_1d
• algebra_solver
• algebra_solver_newton
• map_rect

Current Version:

v3.3.0

[charlesm93]

Examining the code, it looks like algebra_solver and algebra_solver_newton have variadic arguments (@jgaeb implemented this a bit ago).

That said I can't find the issue nor the PR where these changes were made. And it doesn't look like these changes made it all the way to the Stan language.

[nhuurre]

Algebra solvers were made variadic as a side effect of #2421 but that has not been exposed to the Stan language.

[WardBrian]

There is a newer more specific issue for this, closing