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/api/handlers/v0/edit_test.go

@@ -22,7 +22,7 @@ import (
 
 func TestEditServerEndpoint(t *testing.T) {
 	// Create registry service and insert a common test server
-	registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+	registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 
 	// Publish a test server that will be used across test cases
 	testServer := apiv0.ServerJSON{

internal/api/handlers/v0/publish_integration_test.go

@@ -46,7 +46,7 @@ func TestPublishIntegration(t *testing.T) {
 	}
 
 	// Setup fake service
-	registryService := service.NewRegistryService(database.NewMemoryDB(), testConfig)
+	registryService := service.NewRegistryService(database.NewTestDB(t), testConfig)
 
 	// Create a new ServeMux and Huma API
 	mux := http.NewServeMux()

internal/api/handlers/v0/publish_registry_validation_test.go

@@ -34,7 +34,7 @@ func TestPublishRegistryValidation(t *testing.T) {
 	}
 
 	// Setup fake service
-	registryService := service.NewRegistryService(database.NewMemoryDB(), testConfig)
+	registryService := service.NewRegistryService(database.NewTestDB(t), testConfig)
 
 	// Create a new ServeMux and Huma API
 	mux := http.NewServeMux()

internal/api/handlers/v0/publish_test.go

@@ -357,7 +357,7 @@ func TestPublishEndpoint(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			// Create registry service
-			registryService := service.NewRegistryService(database.NewMemoryDB(), testConfig)
+			registryService := service.NewRegistryService(database.NewTestDB(t), testConfig)
 
 			// Setup registry service
 			tc.setupRegistryService(registryService)
@@ -459,7 +459,7 @@ func TestPublishEndpoint_MultipleSlashesEdgeCases(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			// Create registry service
-			registryService := service.NewRegistryService(database.NewMemoryDB(), testConfig)
+			registryService := service.NewRegistryService(database.NewTestDB(t), testConfig)
 
 			// Create a new ServeMux and Huma API
 			mux := http.NewServeMux()

internal/api/handlers/v0/servers_test.go

@@ -286,7 +286,7 @@ func TestServersListEndpoint(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			// Create mock registry service
-			registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+			registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 			tc.setupRegistryService(registryService)
 
 			// Create a new test API
@@ -378,7 +378,7 @@ func TestServersListEndpoint(t *testing.T) {
 
 func TestServersDetailEndpoint(t *testing.T) {
 	// Create mock registry service
-	registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+	registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 
 	// Publish multiple versions of the same server
 	testServer1, err := registryService.Publish(apiv0.ServerJSON{
@@ -488,7 +488,7 @@ func TestServersDetailEndpoint(t *testing.T) {
 
 func TestServersVersionsEndpoint(t *testing.T) {
 	// Create mock registry service
-	registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+	registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 
 	// Publish multiple versions of the same server
 	testServer1, err := registryService.Publish(apiv0.ServerJSON{
@@ -598,7 +598,7 @@ func TestServersVersionsEndpoint(t *testing.T) {
 // TestServersEndpointsIntegration tests the servers endpoints with actual HTTP requests
 func TestServersEndpointsIntegration(t *testing.T) {
 	// Create mock registry service
-	registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+	registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 
 	// Test data - publish a server and get its actual ID
 	testServer := apiv0.ServerJSON{

internal/api/handlers/v0/telemetry_test.go

@@ -21,7 +21,7 @@ import (
 )
 
 func TestPrometheusHandler(t *testing.T) {
-	registryService := service.NewRegistryService(database.NewMemoryDB(), config.NewConfig())
+	registryService := service.NewRegistryService(database.NewTestDB(t), config.NewConfig())
 	server, err := registryService.Publish(apiv0.ServerJSON{
 		Name:        "io.github.example/test-server",
 		Description: "Test server detail",