Garbage collect blobs from file system

[sandreae]

We already garbage collect unused blob views from the database, this PR implements garbage collecting blob views from the file system as well. This occurs both when a blob view is not the current view or pinned from another document, and for the current view as well when the blob document itself is not related to by any other document.

During implementation I did a little general renaming/refactoring in the garbage collection task to help code comprehension.

📋 Checklist

• [x] Add tests that cover your changes
• [x] Add this PR to the Unreleased section in CHANGELOG.md
• [x] Link this PR to any issues it closes
• [x] New files contain a SPDX license header

[codecov[bot]]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (3ac8b70) 92.43% compared to head (93ba503) 92.47%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #571 +/- ## ========================================== + Coverage 92.43% 92.47% +0.03% ========================================== Files 106 106 Lines 18164 18396 +232 ========================================== + Hits 16790 17011 +221 - Misses 1374 1385 +11 ``` | [Files](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda) | Coverage Δ | | |---|---|---| | [aquadoggo/src/db/stores/blob.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy9kYi9zdG9yZXMvYmxvYi5ycw==) | `98.18% <100.00%> (+<0.01%)` | :arrow_up: | | [aquadoggo/src/db/stores/document.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy9kYi9zdG9yZXMvZG9jdW1lbnQucnM=) | `98.76% <100.00%> (-0.07%)` | :arrow_down: | | [aquadoggo/src/materializer/tasks/reduce.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy9tYXRlcmlhbGl6ZXIvdGFza3MvcmVkdWNlLnJz) | `94.92% <0.00%> (ø)` | | | [aquadoggo/src/test\_utils/node.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy90ZXN0X3V0aWxzL25vZGUucnM=) | `95.00% <97.29%> (+0.35%)` | :arrow_up: | | [...doggo/src/materializer/tasks/garbage\_collection.rs](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda#diff-YXF1YWRvZ2dvL3NyYy9tYXRlcmlhbGl6ZXIvdGFza3MvZ2FyYmFnZV9jb2xsZWN0aW9uLnJz) | `97.80% <95.40%> (-0.83%)` | :arrow_down: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/p2panda/aquadoggo/pull/571/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda)

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[sandreae]

Very concise useful Postgres error in the CI: Error: The operation was canceled.