✨ Support basic keyword search for OPDS v1.2

[aaronleopold]

Resolves #552

The linked issue is marked as a bug, but really this just wasn't implemented 😛 I'll leave as a draft until I resolve a quirk with Panels, I wrote a note for it in the code. For those following and interested, I posted about it in the Panels discord.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 191 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
core/src/opds/v1_2/feed.rs	0.00%	87 Missing ⚠️
apps/server/src/routers/opds/v1_2.rs	0.00%	83 Missing ⚠️
core/src/opds/v1_2/opensearch.rs	0.00%	18 Missing ⚠️
core/src/db/query/pagination.rs	0.00%	3 Missing ⚠️

Files with missing lines	Coverage Δ
core/src/db/query/pagination.rs	0.00% <0.00%> (ø)
core/src/opds/v1_2/opensearch.rs	0.00% <0.00%> (ø)
apps/server/src/routers/opds/v1_2.rs	0.00% <0.00%> (ø)
core/src/opds/v1_2/feed.rs	34.66% <0.00%> (+0.80%)	⬆️

... and 5 files with indirect coverage changes

[aaronleopold]

After discussions, it appears this is not necessarily an issue with Stump. I'll merge this as-is, with tentative future changes depending on whether pagination for search results in Panels requires it

[tmenguy]

great! thx a lot, what is teh panel issue?

[tmenguy]

(will look into their discord too)