fix: OverflowError matplotlib

[Hussein-Mahfouz]

This should fix the matplotlib OverflowError reported by @sgreenbury when running for London

OverflowError: Exceeded cell block limit in Agg.  Please set the value of rcParams['agg.path.chunksize'], (currently 0) to be greater than 100 or increase the path simplification threshold(rcParams['path.simplify_threshold'] = 0.111111111111 by default and path.simplify_threshold = 0.111111111111 on the input).
Error: Command '['python', 'scripts/3.3_assign_facility_all.py', '--config-file', 'config/2025-03-25_greater-london_msoa_new_regions_01_2020.toml']' returned non-zero exit status 1.