Freq table hierarchical

[CarwilB]

This pull request introduces significant new functionality for generating hierarchical (two-layer) frequency tables, including both data and formatted HTML outputs, and updates the package to support these features. It also adds a new president to the dataset and improves documentation. The most important changes are grouped below by theme.

New hierarchical frequency table functionality

• Added new functions: insert_rows_by_group_vars, two_layer_frequency_table, and two_layer_frequency_kable in R/freq-table-hierarchical.R to support creation and formatting of two-layer frequency tables, along with their documentation (man/insert_rows_by_group_vars.Rd, man/two_layer_frequency_table.Rd, man/two_layer_frequency_kable.Rd). [1] [2] [3] [4]
• Exported the new functions in NAMESPACE and registered necessary imports from janitor and kableExtra for table formatting and manipulation. [1] [2] [3] [4] [5]

Data and documentation updates

• Added a new president ("Rodrigo Paz") to the president levels in data-raw/level-variables.R and updated the presidency name table in data-raw/presidency-name-table.csv to reflect this addition and adjusted the term for "Luis Arce". [1] [2]
• Improved and clarified documentation for the presidency_name_table dataset and its fields, including handling of the most recent presidency's last_day value. [1] [2]

Package metadata

• Bumped the package version to 0.0.0.9012 in DESCRIPTION to reflect these new features and updates.