Review Ingestor/Analyzer error paths

[finestructure]

I need to rework both stages around their error handling. There are still gaps where errors are not caught, for instance this test fails:

    func test_invalidPackageCachePath() throws {
        // setup
        try savePackages(on: app.db, ["1", "2"], processingStage: .ingestion)

        // MUT
        try analyze(application: app, limit: 10).wait()

        // validation
        let packages = try Package.query(on: app.db).sort(\.$url).all().wait()
        XCTAssertEqual(packages.map(\.status), [.invalidUrl, .invalidUrl])
    }

by raising an invalidPackageCachePath exception out of the analyze call that should not bubble up.

In practise this might not happen, because an invalid url like that doesn't get this far in the chain. However, both stages, suffer from being written in the first few days and contain a mix of throwing and Result code which is hard to reason about.

Explore rewriting everthing around Result, if possible.