feat: Add download_all_layers function

[popogis24]

Add download_all_layers function

This PR adds a new function that allows users to download all available geobr layers at once.

Features

• New download_all_layers function that downloads all available layers using their default years
• Support for two output formats:
  • GeoJSON (default)
  • GPKG (GeoPackage)
• Configurable output folder (defaults to 'geobr_layers')
• Proper error handling and driver validation
• Comprehensive test coverage

Example Usage

from geobr import download_all_layers

Download all layers in GeoJSON format (default)
download_all_layers()

Download all layers in GeoPackage format
download_all_layers(driver="GPKG")

Download to a custom folder
download_all_layers(output_folder="my_layers")

[rafapereirabr]

Thanks for the PR, @popogis24 . I'm not sure, though, this is function we should have. What exactly is the use case here ?

[popogis24]

The main use case for this function is to streamline the process of downloading all available geobr layers in a single step, ensuring users have a local copy of the complete dataset without needing to call multiple functions manually.
This is particularly useful for applications that require offline access to geospatial data or for batch processing workflows where multiple layers are needed at once.

For example, I have a system that requires a spatial database to be always up to date, and this function would help me ensure that the latest data is downloaded automatically, without needing to do it manually.