Socrates loads numerous configuration files for parsing on every rank

Socrates loads numerous configuration files for parsing

Each rank in the run and then in the ensemble targets the same files, e.g.:
* [ga9 files](https://github.com/MetOffice/socrates/blob/main/data/spectra/ga9)
* 1-per-rank
* spec/sp_sw_ga9, spec/sp_sw_ga9_k, spec/sp_lw_ga9, spec/sp_lw_ga9_k, spec/mcica_data
* some of these are ~large: `mcica_data`: 2.03MB
* sp_sw_ga9_var (not in source)
* 4-per-rank

Consider providing a rad pattern that either uses:
* MPI-IO to conduct collective reads
* Reads on `Rank0` and distributes to ranks using MPI