updated interface for accumulation

[sbfnk]

Description

This PR closes #547 following the design agreed in #839.

Initial submission checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have tested my changes locally (using devtools::test() and devtools::check()).
• I have added or updated unit tests where necessary.
• I have updated the documentation if required and rebuilt docs if yes (using devtools::document()).
• I have followed the established coding standards (and checked using lintr::lint_package()).
• I have added a news item linked to this PR.

After the initial Pull Request

• I have reviewed Checks for this PR and addressed any issues as far as I am able.

[github-actions]

Table: Benchmarking results (mean time in seconds).

operation	branch	main	% change	range	trend
reports	5	5	0	(-5, 3)	no change
delays	4	4	1	(-2, 4)	no change
report lp	3.9	3.9	1	(-1, 12)	no change
infections	3.2	3.1	1	(-8, 11)	no change
R	1.5	1.5	1	(-3, 7)	no change
update gp	1.2	1.2	2	(-5, 11)	no change
gt	0.51	0.5	0	(-8, 10)	no change
day of the week	0.48	0.48	0	(-9, 7)	no change
truncation	0.34	0.34	0	(-9, 7)	no change
rt lp	0.27	0.26	1	(-17, 18)	no change
truncate	0.26	0.26	-2	(-13, 8)	no change
gp lp	0.25	0.24	1	(-8, 11)	no change
delays lp	0.14	0.13	4	(-11, 24)	no change
generated quantities	0.0083	0.0071	14	(7, 23)	slowdown
assign max	5.8e-07	4.1e-07	25	(-59, 69)	no change

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 08814c4 is merged into main:

• 🚀default: 33.8s -> 28.8s [-25.29%, -4.1%]
• ✔️no_delays: 38.5s -> 41.6s [-14.28%, +30.1%]
• ✔️random_walk: 10.5s -> 10.2s [-23.69%, +19.63%]
• ✔️stationary: 17.5s -> 22.3s [-5.28%, +61.03%]
• ✔️uncertain: 51s -> 52.6s [-16.78%, +23.37%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[sbfnk]

Thanks for the comments/suggestions - I've updated the argument names as suggested and did a pass through the docs in an attempt to make them clearer.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if fd020b6 is merged into main:

• ✔️default: 22.6s -> 22.7s [-8.54%, +9.48%]
• ✔️no_delays: 26.7s -> 26.2s [-10.93%, +7.56%]
• ✔️random_walk: 9.28s -> 9.46s [-5.99%, +9.79%]
• ✔️stationary: 13.1s -> 11.3s [-35.7%, +7.21%]
• ✔️uncertain: 37.6s -> 38s [-5.96%, +7.72%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 9a8ef8e is merged into main:

• ✔️default: 23.5s -> 21.3s [-28.56%, +9.77%]
• ✔️no_delays: 28.6s -> 27.5s [-15%, +7.19%]
• ✔️random_walk: 19.2s -> 9.96s [-154.71%, +58.64%]
• ✔️stationary: 13.7s -> 13.1s [-28.71%, +20.62%]
• ✔️uncertain: 38.4s -> 40.4s [-0.88%, +11.28%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[seabbs]

This looks good to me and happy for it to be merged. I have a open comment with a last check about the interaction between accumulation and truncation (which I think I already raised and so is likely easy to dismiss)

[seabbs]

CI failures are unrelated to this PR (trying and failing to download R) so I am happy to ignore them

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if abb8d1c is merged into main:

• ✔️default: 21.1s -> 22.5s [-5.7%, +18.67%]
• ✔️no_delays: 27.1s -> 27.1s [-12.33%, +12.42%]
• ✔️random_walk: 9.71s -> 9.64s [-8.15%, +6.67%]
• ✔️stationary: 12.7s -> 13.3s [-15.82%, +24.18%]
• ✔️uncertain: 36.6s -> 35.6s [-18.18%, +12.48%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if fc91c49 is merged into main:

• ✔️default: 22s -> 23.7s [-4.21%, +20%]
• ✔️no_delays: 28s -> 27.2s [-13.23%, +7.8%]
• ✔️random_walk: 9.68s -> 9.8s [-7.5%, +10.05%]
• ✔️stationary: 13s -> 12.9s [-19.13%, +17.62%]
• ✔️uncertain: 38.9s -> 37.6s [-15.24%, +8.41%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[sbfnk]

Thanks all for the comments/reviews - merging now as failed checks are unrelated.