Add unit tests for SBOM ingestion and transformation

- Implement `SbomIngestServiceCollectionExtensionsTests` to verify the SBOM ingestion pipeline exports snapshots correctly.
- Create `SbomIngestTransformerTests` to ensure the transformation produces expected nodes and edges, including deduplication of license nodes and normalization of timestamps.
- Add `SbomSnapshotExporterTests` to test the export functionality for manifest, adjacency, nodes, and edges.
- Introduce `VexOverlayTransformerTests` to validate the transformation of VEX nodes and edges.
- Set up project file for the test project with necessary dependencies and configurations.
- Include JSON fixture files for testing purposes.

src/Findings/StellaOps.Findings.Ledger/Infrastructure/Postgres/LedgerDataSource.cs

@@ -0,0 +1,81 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Npgsql;
+using StellaOps.Findings.Ledger.Options;
+
+namespace StellaOps.Findings.Ledger.Infrastructure.Postgres;
+
+public sealed class LedgerDataSource : IAsyncDisposable
+{
+    private readonly NpgsqlDataSource _dataSource;
+    private readonly LedgerServiceOptions.DatabaseOptions _options;
+    private readonly ILogger<LedgerDataSource> _logger;
+
+    public LedgerDataSource(
+        IOptions<LedgerServiceOptions> options,
+        ILogger<LedgerDataSource> logger)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        _options = options.Value.Database;
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+
+        var builder = new NpgsqlDataSourceBuilder(_options.ConnectionString);
+        _dataSource = builder.Build();
+    }
+
+    public int CommandTimeoutSeconds => _options.CommandTimeoutSeconds;
+
+    public async ValueTask DisposeAsync()
+    {
+        await _dataSource.DisposeAsync().ConfigureAwait(false);
+    }
+
+    public Task<NpgsqlConnection> OpenConnectionAsync(string tenantId, CancellationToken cancellationToken)
+        => OpenConnectionInternalAsync(tenantId, cancellationToken);
+
+    private async Task<NpgsqlConnection> OpenConnectionInternalAsync(string tenantId, CancellationToken cancellationToken)
+    {
+        var connection = await _dataSource.OpenConnectionAsync(cancellationToken).ConfigureAwait(false);
+
+        try
+        {
+            await ConfigureSessionAsync(connection, tenantId, cancellationToken).ConfigureAwait(false);
+        }
+        catch
+        {
+            await connection.DisposeAsync().ConfigureAwait(false);
+            throw;
+        }
+
+        return connection;
+    }
+
+    private async Task ConfigureSessionAsync(NpgsqlConnection connection, string tenantId, CancellationToken cancellationToken)
+    {
+        try
+        {
+            await using (var command = new NpgsqlCommand("SET TIME ZONE 'UTC';", connection))
+            {
+                command.CommandTimeout = _options.CommandTimeoutSeconds;
+                await command.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
+            }
+
+            if (!string.IsNullOrWhiteSpace(tenantId))
+            {
+                await using var tenantCommand = new NpgsqlCommand("SELECT set_config('app.current_tenant', @tenant, false);", connection);
+                tenantCommand.CommandTimeout = _options.CommandTimeoutSeconds;
+                tenantCommand.Parameters.AddWithValue("tenant", tenantId);
+                await tenantCommand.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
+            }
+        }
+        catch (Exception ex)
+        {
+            if (_logger.IsEnabled(LogLevel.Error))
+            {
+                _logger.LogError(ex, "Failed to configure PostgreSQL session for tenant {TenantId}.", tenantId);
+            }
+
+            throw;
+        }
+    }
+}