Missing intermediate output files for TC/grid analysis

[thomas-fred]

Three kinds of output file for the TC/grid analysis are not being produced for a subset of marginal (seldom hit) countries. The files are:

• length_m_by_edge
• length_m_by_event
• pop_affected_by_event

e.g. results/power/by_country/AND/exposure/STORM-HadGEM3-GC31-HM/length_m_by_event.pq which is required by the rule exposure_by_admin_region. If it's not present, snakemake will error.

We should either:

1. Produce these missing, empty files
2. Modify the upstream rules to be robust to them missing

Option 1) is probably easier, given how snakemake works

Rather than solve this when running the TC/grid analysis, I used some hacky scripts to write empty files where necessary. For more details see this file and the scripts next to it on the linux cluster: /soge-home/projects/mistral/archive/tc_grid_2024/2024-04-12T155923+0100/handle_missing_outputs/README.md