Improve CI coverage reporting

This MR adds a coverage CI job to aggregate the coverage reports from all of the test jobs, which is much better than gitlab's naive mean average calculation.

added 1 commit

• 332e393b - ci: add coverage job to combine reports

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added 7 commits

• 332e393b...7dde916b - 5 commits from branch computing/gwdatafind:main
• f7a1331b - pyproject.toml: add coverage:paths
• 82430e99 - ci: add coverage job to combine reports

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added 4 commits

• 82430e99...54f1bbce - 2 commits from branch computing/gwdatafind:main
• 8c8a5970 - pyproject.toml: add coverage:paths
• 9d993dd2 - ci: add coverage job to combine reports

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added 2 commits

• 90dead61 - pyproject.toml: add coverage:paths
• fc421889 - ci: add coverage job to combine reports

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mentioned in commit 002aec6b

merged