Fix invalid height/width attributes in Rd figures

CRAN checks report a NOTE regarding the use of non-pixel height and width attributes in Rd figure options.

The NOTE highlights that the \figure{} directive in Rd files uses width or height attributes set in percentages or other units instead of pixels, violating the HTML5 standard.
Replace non-pixel attributes with CSS style attributes in the options: argument, as advised by CRAN.

Current code

\figure{airGRdatasets-map-catchments.png}{options: width="60\%" alt="Figure: airGRdatasets-map-catchments.png"}

Corrected code

\figure{airGRdatasets-map-catchments.png}{options: style="width: 60\%;" alt="Figure: airGRdatasets-map-catchments.png"}