Fix db_to_cache details and add commit_id to item metadata queries

[manuelma]

Fixes a couple of queries plus other minor details.

Checklist before merging

• [ ] Documentation (also in Toolbox repo) is up-to-date
• [ ] Release notes in Toolbox repo have been updated
• [ ] Unit tests have been added/updated accordingly
• [ ] Code has been formatted by black
• [ ] Unit tests pass

[codecov-commenter]

Codecov Report

Base: 74.45% // Head: 74.46% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (61cbf5e) compared to base (9598974). Patch coverage: 55.55% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #191 +/- ## ======================================= Coverage 74.45% 74.46% ======================================= Files 71 71 Lines 11691 11693 +2 Branches 2145 2145 ======================================= + Hits 8705 8707 +2 - Misses 2534 2536 +2 + Partials 452 450 -2 ``` | [Impacted Files](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/191?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project) | Coverage Δ | | |---|---|---| | [spinedb\_api/db\_mapping\_base.py](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/191/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project#diff-c3BpbmVkYl9hcGkvZGJfbWFwcGluZ19iYXNlLnB5) | `83.29% <20.00%> (+0.03%)` | :arrow_up: | | [spinedb\_api/db\_mapping\_add\_mixin.py](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/191/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project#diff-c3BpbmVkYl9hcGkvZGJfbWFwcGluZ19hZGRfbWl4aW4ucHk=) | `80.14% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project)

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