suppress load_survey() 'No reference provided' warning

Add warning = FALSE to all chunk headers that call
contactsurveys::download_survey() + socialmixr::load_survey(),
suppressing the cosmetic 'No reference provided' warning from socialmixr.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: avallecam

episodes/compare-interventions.Rmd

@@ -360,7 +360,7 @@ output <- epidemics::model_vacamole(
 
 1.  Run the model
 
-```{r}
+```{r, message = FALSE, warning = FALSE}
 survey_files_2 <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",
   verbose = FALSE

episodes/contact-matrices.Rmd

@@ -83,7 +83,7 @@ Contact matrices are commonly estimated from studies that use diaries to record
 
 The R package `{socialmixr}` contains functions which can estimate contact matrices from POLYMOD and other surveys. We can download and load the POLYMOD survey data directly from Zenodo using `{contactsurveys}` and `{socialmixr}`:
 
-```{r polymod_, echo = TRUE, message = FALSE}
+```{r polymod_, echo = TRUE, message = FALSE, warning = FALSE}
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",
   verbose = FALSE
@@ -201,7 +201,7 @@ Similar to the code above, to access vector values within a dataframe, you can u
 
 :::::::::::::::::::::::: instructor 
 
-```{r zambia_solution}
+```{r zambia_solution, message = FALSE, warning = FALSE}
 # Generate the contact matrix for Zambia only
 contacts_byage_zambia <- socialmixr::contact_matrix(
   survey = zambia_sa_survey,

episodes/disease-burden.Rmd

@@ -83,7 +83,7 @@ We'll use `{epiparameter}` to define these delay distributions. The Gamma distri
 
 :::::::::::::::: instructor
 
-```{r, echo = TRUE, message = FALSE}
+```{r, echo = TRUE, message = FALSE, warning = FALSE}
 # download and load contact and population data from Zenodo
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",

episodes/modelling-interventions.Rmd

@@ -85,7 +85,7 @@ We will investigate the effect of interventions on a COVID-19 outbreak using an
 
 The SEIR model divides the population into four compartments: Susceptible (S), Exposed (E), Infectious (I), and Recovered (R). We will set the following parameters for our model: $R_0 = 2.7$ (basic reproduction number), latent period or pre-infectious period $= 4$ days, and the infectious period $= 5.5$ days (parameters adapted from [Davies et al. (2020)](https://doi.org/10.1016/S2468-2667(20)30133-X)). We adopt a contact matrix with age bins 0-18, 18-65, 65 years and older using `{socialmixr}`, and assume that one in every 1 million individuals in each age group is infectious at the start of the epidemic.
 
-```{r model_setup, echo = TRUE, message = FALSE}
+```{r model_setup, echo = TRUE, message = FALSE, warning = FALSE}
 # download and load survey data
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",

episodes/simulating-transmission.Rmd

@@ -196,7 +196,7 @@ Use the POLYMOD survey available at `https://doi.org/10.5281/zenodo.3874557`
 
 :::::::::::::::::::::::: solution 
 
-```{r polymod_uk, echo = TRUE, message = FALSE}
+```{r polymod_uk, echo = TRUE, message = FALSE, warning = FALSE}
 # Download and load the contact survey data
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",

episodes/template.Rmd

@@ -86,7 +86,7 @@ contacts_byage
 
 ## Output
 
-```{r polymod_uk, echo = FALSE, message = FALSE}
+```{r polymod_uk, echo = FALSE, message = FALSE, warning = FALSE}
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",
   verbose = FALSE
@@ -130,7 +130,7 @@ Load contact and population data for Poland from the POLYMOD Zenodo survey using
 
 :::::::::::::::::::::::: solution 
 
-```{r polymod_poland, message = FALSE}
+```{r polymod_poland, message = FALSE, warning = FALSE}
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",
   verbose = FALSE

episodes/vaccine-comparisons.Rmd

@@ -67,7 +67,7 @@ We will illustrate this using results from `model_default()` in `{epidemics}`. T
 + vaccination program 02: vaccination rate 0.01.
 
 
-```{r, echo = FALSE, message = FALSE}
+```{r, echo = FALSE, message = FALSE, warning = FALSE}
 survey_files <- contactsurveys::download_survey(
   survey = "https://doi.org/10.5281/zenodo.3874557",
   verbose = FALSE