findContentRootByUri fails with serialization error

[johnsonr]

This is important because it will affect refresh of content for guide users

[jasperblues]

Added test cases for a few scenarios, including one that didn't previously pass - that's for a ContentRoot that doesn't have Chunk or Document labels, which was possible at least according to the method implementation.

If it still happens will need more specific repro steps.

@Test
    fun `should find content root by uri for Document node`() {
        val uri = "test://document-node-${UUID.randomUUID()}"
        createTestNode(listOf("ContentElement", "Document"), uri)

        val result = drivineStore.findContentRootByUri(uri)

        println("Found Document content root: $result")
        assertNotNull(result, "Expected to find a ContentRoot with Document label and URI: $uri")
    }

    @Test
    fun `should find content root by uri for Document with Section labels`() {
        val uri = "test://document-section-${UUID.randomUUID()}"
        createTestNode(listOf("ContentElement", "Document", "Section", "ContainerSection"), uri)

        val result = drivineStore.findContentRootByUri(uri)

        println("Found Document+Section content root: $result")
        assertNotNull(result, "Expected to find a ContentRoot with Document+Section labels and URI: $uri")
    }

    @Test
    fun `should find content root by uri for ContentRoot label without Document`() {
        val uri = "test://content-root-only-${UUID.randomUUID()}"
        createTestNode(listOf("ContentElement", "ContentRoot"), uri)

        val result = drivineStore.findContentRootByUri(uri)

        println("Found ContentRoot (no Document label): $result")
        assertNotNull(result, "Expected to find a ContentRoot with ContentRoot label (no Document) and URI: $uri")
    }

    @Test
    fun `should return null for non-existent uri`() {
        val uri = "test://non-existent-${UUID.randomUUID()}"

        val result = drivineStore.findContentRootByUri(uri)

        assertNull(result, "Expected null for non-existent URI")
    }

    @Test
    fun `should not find Chunk node as content root`() {
        val uri = "test://chunk-node-${UUID.randomUUID()}"
        createTestNode(listOf("ContentElement", "Chunk"), uri)

        val result = drivineStore.findContentRootByUri(uri)

        assertNull(result, "Chunk nodes should not be returned as ContentRoot")
    }