compile_reactions: Precompile the reactions
In GillespieSSA2: Gillespie's Stochastic Simulation Algorithm for Impatient People

By precompiling the reactions, you can run multiple SSA simulations repeatedly without having to recompile the reactions every time.

compile_reactions(
  reactions,
  state_ids,
  params,
  buffer_ids = NULL,
  hardcode_params = FALSE,
  fun_by = 10000L
)

`reactions`	'reaction' A list of multiple `reaction()` objects.
`state_ids`	`[character]` The names of the states in the correct order.
`params`	`[named numeric]` Constants that are used in the propensity functions.
`buffer_ids`	`[character]` The order of any buffer calculations that are made as part of the propensity functions.
`hardcode_params`	`[logical]` Whether or not to hardcode the values of `params` in the compilation of the propensity functions. Setting this to `TRUE` will result in a minor sacrifice in accuracy for a minor increase in performance.
`fun_by`	`[integer]` Combine this number of propensity functions into one function.

A list of objects solely to be used by ssa().

x[["state_change"]]: A sparse matrix of reaction effects.
x[["reaction_ids"]]: The names of the reactions.
x[["buffer_ids"]]: A set of buffer variables found in the propensity functions.
x[["buffer_size"]]: The minimum size of the buffer required.
x[["function_pointers"]]: A list of compiled propensity functions.
x[["hardcode_params"]]: Whether the parameters were hard coded into the source code.'