Remove the in-memory database (#537)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The follow PR removes the in-memory database option from the registry.

We had a chat about this with @domdomegg and although it is supposed to
be convenient, it isn't that useful in reality. We want to test and
develop the registry in a setup that is closer to the environment it is
supposed to be run. One of the main reasons are:
* We don't use it anywhere else besides unit testing and potentially
local development. Instead we should use postgresql for reliable results
(in-memory was actually giving false positive results)
* We have to keep maintaining it and make sure it mimics the behaviour
we have for postgresql which is not yielding a lot of value

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
Yes, I've updated the test unit make target to run in the postgresql
environment and now we can see the race condition issue happening.

## Breaking Changes
<!-- Will users need to update their code or configurations? -->
No

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

internal/importer/importer_test.go

@@ -49,15 +49,15 @@ func TestImportService_LocalFile(t *testing.T) {
 	require.NoError(t, err)
 	defer os.Remove(tempFile)
 
-	memDB := database.NewMemoryDB()
+	testDB := database.NewTestDB(t)
 
 	// Create importer service and test import
-	service := importer.NewService(memDB)
+	service := importer.NewService(testDB)
 	err = service.ImportFromPath(context.Background(), tempFile)
 	require.NoError(t, err)
 
 	// Verify the server was imported
-	servers, _, err := memDB.List(context.Background(), nil, "", 10)
+	servers, _, err := testDB.List(context.Background(), nil, "", 10)
 	require.NoError(t, err)
 	assert.Len(t, servers, 1)
 	assert.Equal(t, "io.github.test/test-server-1", servers[0].Name)
@@ -93,15 +93,15 @@ func TestImportService_HTTPFile(t *testing.T) {
 	}))
 	defer server.Close()
 
-	memDB := database.NewMemoryDB()
+	testDB := database.NewTestDB(t)
 
 	// Create importer service and test import
-	service := importer.NewService(memDB)
+	service := importer.NewService(testDB)
 	err := service.ImportFromPath(context.Background(), server.URL+"/seed.json")
 	require.NoError(t, err)
 
 	// Verify the server was imported
-	servers, _, err := memDB.List(context.Background(), nil, "", 10)
+	servers, _, err := testDB.List(context.Background(), nil, "", 10)
 	require.NoError(t, err)
 	assert.Len(t, servers, 1)
 	assert.Equal(t, "io.github.test/http-test-server", servers[0].Name)
@@ -121,7 +121,7 @@ func TestImportService_RegistryAPI(t *testing.T) {
 			Version: "1.0.0",
 			Meta: &apiv0.ServerMeta{
 				Official: &apiv0.RegistryExtensions{
-					ServerID:    "server-id-test",
+					ServerID:    "server-id-test-1",
 					VersionID:   "api-test-id-1",
 					PublishedAt: time.Now(),
 					UpdatedAt:   time.Now(),
@@ -140,7 +140,7 @@ func TestImportService_RegistryAPI(t *testing.T) {
 			Version: "2.0.0",
 			Meta: &apiv0.ServerMeta{
 				Official: &apiv0.RegistryExtensions{
-					ServerID:    "server-id-test",
+					ServerID:    "server-id-test-2",
 					VersionID:   "api-test-id-2",
 					PublishedAt: time.Now(),
 					UpdatedAt:   time.Now(),
@@ -179,15 +179,15 @@ func TestImportService_RegistryAPI(t *testing.T) {
 	}))
 	defer server.Close()
 
-	memDB := database.NewMemoryDB()
+	testDB := database.NewTestDB(t)
 
 	// Create importer service and test import
-	service := importer.NewService(memDB)
+	service := importer.NewService(testDB)
 	err := service.ImportFromPath(context.Background(), server.URL+"/v0/servers")
 	require.NoError(t, err)
 
 	// Verify both servers were imported
-	servers, _, err := memDB.List(context.Background(), nil, "", 10)
+	servers, _, err := testDB.List(context.Background(), nil, "", 10)
 	require.NoError(t, err)
 	assert.Len(t, servers, 2)