Update MSOA coverage dataset

[fcorowe]

Summary

• refresh coverage_msoa from the current active-population-bias source file
• update packaged RDA, normalized CSV, source metadata, checksums, and row count
• allow coverage_msoa to be a valid subset of packaged MSOA covariates rather than requiring exact full coverage

Data update

• source: /Volumes/DEBIAS/data/outputs/mapp2/census-month/populations/active-population-bias/coverage_msoa.rda
• valid packaged rows: 6,906
• source SHA-256: e3a8618087177d4aee43b60848b929fb63fd006c49a3d087a3b010aa240500f9

Validation

• devtools::test(): 213 passed, 0 failed
• source checksum matches metadata
• git diff --check

Closes #13