replace from "probability" to "proportion" in superspreading episode

On episode "account superspreading" (specifically in [this section](https://epiverse-trace.github.io/tutorials-middle/superspreading-estimate.html#probability-of-cases-in-a-given-cluster)) we interpret `proportion_cluster_size` as:

> estimate the probability of having a cluster of secondary infections caused by a primary case identified by backward tracing of size $X$ or larger ([Endo et al., 2020](https://wellcomeopenresearch.org/articles/5-239/v3))

However, for homogeneity with package documentation ([manual](https://epiverse-trace.github.io/superspreading/reference/proportion_cluster_size.html), [vignette](https://epiverse-trace.github.io/superspreading/articles/epidemic_risk.html?q=proportion_cluster#superspreading-in-decision-making)), we should interpret it as:

> estimate the proportion of new cases originating from a transmission cluster of at least $X$ cases ([Knight et al., 2020](https://assets.publishing.service.gov.uk/media/5eff137ad3bf7f769ba78d25/S0473_SPI-M_Superspreading_and_clusters.pdf)). This estimate can give answer to a question like: how many cases are associated with large clusters? which is useful to assess backward contact training efforts.

Current template to update interpretations in [working branch](https://github.com/epiverse-trace/tutorials-middle/tree/fix-probability-proportion-cluster-size):

``` r
# Larger clusters are likely to be detected
# through backward tracing in the presence of overdispersion

set.seed(33)

# proportion-cluster size ------------------------------------------------

superspreading::proportion_cluster_size(
R = 0.8, k = 0.1, cluster_size = 5
)
#> R k prop_5
#> 1 0.8 0.1 66.2%
# The proportion of new cases originating from
# a cluster of at least 5 secondary cases from a primary case
# is 66%

# The proportion of all transmission event that were part of
# secondary case clusters (i.e., from the same primary case)
# of at least 5 cases
# is 66%

# compare ----------------------------------------------------------------

superspreading::proportion_cluster_size(
R = 0.9, k = 0.02, cluster_size = c(1, 2, 5, 10, 20)
)
#> R k prop_1 prop_2 prop_5 prop_10 prop_20
#> 1 0.9 0.02 100% 98.1% 92.1% 82.9% 66.6%
superspreading::proportion_cluster_size(
R = 0.9, k = 0.1, cluster_size = c(1, 2, 5, 10, 20)
)
#> R k prop_1 prop_2 prop_5 prop_10 prop_20
#> 1 0.9 0.1 100% 91.9% 70.1% 43.4% 14.9%
superspreading::proportion_cluster_size(
R = 0.9, k = 0.4, cluster_size = c(1, 2, 5, 10, 20)
)
#> R k prop_1 prop_2 prop_5 prop_10 prop_20
#> 1 0.9 0.4 100% 80.9% 34.6% 7.11% 0.146%

# the probability of (finding) new cases originating from
# a cluster of at least 5, 10, 20 secondary cases from a primary case
# increases when there is more overtransmission (lower k value)

# proportion-transmission ------------------------------------------------

superspreading::proportion_transmission(
R = 0.8, k = 0.1, percent_transmission = 0.8
)
#> R k prop_80
#> 1 0.8 0.1 8.47%
# The proportion of cases responsible of 80% of transmission
# is 8.47%

# compare ----------------------------------------------------------------

superspreading::proportion_transmission(
R = 0.9, k = 0.02, percent_transmission = 0.8
)
#> R k prop_80
#> 1 0.9 0.02 2.13%
superspreading::proportion_transmission(
R = 0.9, k = 0.1, percent_transmission = 0.8
)
#> R k prop_80
#> 1 0.9 0.1 8.62%
superspreading::proportion_transmission(
R = 0.9, k = 0.4, percent_transmission = 0.8
)
#> R k prop_80
#> 1 0.9 0.4 19.9%
# The proportion of cases responsible of 80% of transmission
# decreases (more concentrated in a lower proportion of cases)
# when there is more overtransmission (lower k value)
```

^{Created on 2025-04-01 with [reprex v2.1.1](https://reprex.tidyverse.org)}