Experimental parallelisation of Ebola model

[pratikunterwegs]

This draft PR is an experiment in parallelising the Ebola model using the {furrr} package, and is mostly aimed at checking whether this offers any performance gains. Changes:

1. Using furrr::future_map() instead of Map() in .model_ebola_internal();
2. Using {furrr} functionality for parallelisation-safe RNG seeds instead of `withr::local_seed();
3. Setting up a multi-core future resolution plan for continuous benchmarking for futurised version of Ebola model.

[github-actions]

This pull request:

• Adds 6 new dependencies (direct and indirect)
• Adds 1 new system dependencies
• Removes 0 existing dependencies (direct and indirect)
• Removes 0 existing system dependencies

(Note that results may be inacurrate if you branched from an outdated version of the target branch.)

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 21ebc61 is merged into main:

• 🚀default_ode: 14.5ms -> 10.8ms [-29.9%, -21.69%]
• ❗🐌default_ode_interventions: 71.4ms -> 99.5ms [+38.77%, +40.11%]
• ✔️default_ode_param_vec: 827ms -> 818ms [-2.11%, +0.03%]
• 🚀default_ode_paramvec_intervs: 6.24s -> 6.16s [-1.84%, -0.52%]
• 🚀ebola: 599ms -> 462ms [-23.38%, -22.32%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[pratikunterwegs]

Seeing some dubious results on the benchmarking here as the parallelisations appears to speed up the ebola model but the PR also shows performance losses for the ODE model which wasn't touched in this PR. Running the CB again and closing this PR as a useful trial if checks remain unreliable.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if a6e001e is merged into main:

• ✔️default_ode: 10.9ms -> 10.9ms [-1.96%, +1.45%]
• 🚀default_ode_interventions: 99.5ms -> 72.5ms [-27.76%, -26.4%]
• ✔️default_ode_param_vec: 833ms -> 835ms [-0.21%, +0.72%]
• ✔️default_ode_paramvec_intervs: 6.26s -> 6.27s [-0.43%, +0.7%]
• 🚀ebola: 561ms -> 473ms [-17.47%, -13.81%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[pratikunterwegs]

Closing this PR as results remain potentially unreliable, but it might be worth exploring parallelisation again in future.