Implement handling for AGS 4 files

[JoostGevaert]

• Example AGS 4 data from the UK for the Silvertown tunnel project and an example marimo notebook have to be further developed. Data and notebook can be found here: bedrock-ge/examples/uk_silvertown_tunnel_ags4. Have a look at the Kai Tak, HK example for AGS 3 data for inspiration: bedrock-ge/examples/hk_kaitak_ags3/hk_kaitak_ags3_to_brgi_geodb.py
• ags4_to_dfs and ags4_to_brgi_db_mapping need to be implemented in brgi.ags4, similar to brgi.ags3.
• brgi.ags4.ags4_to_dfs needs to be adapted to use AGS4.convert_to_numeric similar to how it's done in the 4th cell of the example marimo notebook (L70 - L82)

[JoostGevaert]

Hi @konnerhorton,
If you wanted to continue working on something during the coming week, I think this issue would be up your alley :)
Jules and I won't touch AGS 4 stuff until after next week, as we're going to a small conference on Free Open-Source Software for Geospatial (FOSS4G) in Wageningen, NL (Geotech Data = 3D Vector Data)

[konnerhorton]

Sounds good, I should have time to get a decent start on it.