🐛 Fix root-level books in collection libraries

[aaronleopold]

Fixes an issue in collection-priority libraries where having a root-level book causes the scanner to create a series with the entire content of the library, effectively duplicating all books in the database.

This is a simple change to just make the scanner aware of this scenario and adjust the indexing depth accordingly.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
core/src/filesystem/scanner/series_scan_job.rs	0.00%	8 Missing ⚠️
core/src/filesystem/scanner/library_scan_job.rs	0.00%	7 Missing ⚠️

Files with missing lines	Coverage Δ
core/src/filesystem/scanner/library_scan_job.rs	0.00% <0.00%> (ø)
core/src/filesystem/scanner/series_scan_job.rs	0.00% <0.00%> (ø)