🚧 Metadata fetching foundations and reworked job system

[aaronleopold]

I started this effort back in January and at this point it has gotten to be larger than I'd like, granted it is a large feature, so I am contemplating a more WIP merge into unstable sooner (probably shortly after I release 0.1.0). I also took about a week to refactor the job system to be able to support cron jobs (e.g., to retry failed metadata fetches at a given schedule), which I would have preferred not mixing with this already large feature.

I'll leave as a draft until I am comfortable enough with the current change-set as an unstable feature, considering the fact that there are no non-breaking change guarantees in that release channel. There is a LOT of work to get it actually ready for even the experimental channel, but now that the foundations are in place I can aim to tackle it more iteratively over the next couple of months.

[codecov]

Codecov Report

❌ Patch coverage is 15.65670% with 3243 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
core/src/filesystem/metadata/apply.rs	0.00%	374 Missing ⚠️
...s/integrations/metadata/src/providers/hardcover.rs	0.00%	259 Missing ⚠️
crates/graphql/src/mutation/series_metadata.rs	0.00%	218 Missing ⚠️
core/src/filesystem/metadata/fetch.rs	0.00%	206 Missing ⚠️
crates/graphql/src/mutation/media_metadata.rs	0.00%	186 Missing ⚠️
core/src/job/state.rs	0.00%	175 Missing ⚠️
crates/graphql/src/loader/author.rs	0.00%	161 Missing ⚠️
crates/graphql/src/object/author.rs	0.00%	156 Missing ⚠️
crates/graphql/src/query/author.rs	0.00%	147 Missing ⚠️
core/src/filesystem/metadata/fetch_job.rs	0.00%	140 Missing ⚠️
... and 57 more

Files with missing lines	Coverage Δ
apps/server/src/config/session/utils.rs	33.33% <ø> (+1.19%)	⬆️
apps/server/src/errors.rs	0.00% <ø> (ø)
.../src/filesystem/image/thumbnail/placeholder_job.rs	0.00% <ø> (ø)
core/src/filesystem/media/analysis/job.rs	0.00% <ø> (ø)
core/src/filesystem/media/builder.rs	81.00% <100.00%> (+0.10%)	⬆️
core/src/job/error.rs	0.00% <ø> (ø)
core/src/job/mod.rs	0.00% <ø> (ø)
core/src/job/output.rs	0.00% <ø> (ø)
core/src/job/progress.rs	0.00% <ø> (ø)
crates/graphql/src/pagination.rs	58.37% <ø> (ø)
... and 72 more

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