feat: track download counts for both cache hits and cache misses

Previously, download counts only incremented on cache hits (when package
was served from cache). First-time downloads (cache misses) were not counted.

Changes:
- Add UpdateDownloadCount() call when serving newly cached packages
- This ensures every download through the proxy increments the counter
- Analytics tracking also added for cache misses

Behavior now:
- First download (cache miss): counter = 1
- Second download (cache hit): counter = 2
- Third download (cache hit): counter = 3
- etc.

Updated all relevant tests to expect the additional UpdateDownloadCount call.

Resolves user requirement: "I want the counters to increase whenever
package is downloaded via proxy - regardless of it being new download
or cached download"

pkg/cache/cache.go

@@ -320,6 +320,22 @@ servePkg:
 		return nil, errors.Wrap(err, errors.ErrCodeStorageFailure, "failed to retrieve just-stored package")
 	}
 
+	// Track download count for first-time download (cache miss)
+	// This ensures download count increments regardless of cache hit/miss
+	if err := m.metadata.UpdateDownloadCount(ctx, registry, name, version); err != nil {
+		log.Warn().
+			Err(err).
+			Str("registry", registry).
+			Str("package", name).
+			Str("version", version).
+			Msg("Failed to update download count for newly cached package")
+	}
+
+	// Track download in analytics if enabled
+	if m.analytics != nil {
+		m.trackDownload(registry, name, version, storedPkg.Size)
+	}
+
 	return &CacheEntry{
 		Package:     storedPkg,
 		Data:        storedData,

pkg/cache/cache_test.go

@@ -343,6 +343,7 @@ func TestGet(t *testing.T) {
 				s.On("Put", mock.Anything, "npm/lodash/4.17.21", mock.Anything, mock.Anything).Return(nil)
 				m.On("SavePackage", mock.Anything, mock.Anything).Return(nil)
 				s.On("Get", mock.Anything, "npm/lodash/4.17.21").Return(io.NopCloser(strings.NewReader("upstream data")), nil)
+				m.On("UpdateDownloadCount", mock.Anything, "npm", "lodash", "4.17.21").Return(nil)
 			},
 			fetchFunc: func(ctx context.Context) (io.ReadCloser, string, error) {
 				return io.NopCloser(strings.NewReader("upstream data")), "https://registry.npmjs.org/lodash", nil
@@ -374,6 +375,7 @@ func TestGet(t *testing.T) {
 				s.On("Put", mock.Anything, "npm/expired-pkg/1.0.0", mock.Anything, mock.Anything).Return(nil)
 				m.On("SavePackage", mock.Anything, mock.Anything).Return(nil)
 				s.On("Get", mock.Anything, "npm/expired-pkg/1.0.0").Return(io.NopCloser(strings.NewReader("refreshed data")), nil)
+				m.On("UpdateDownloadCount", mock.Anything, "npm", "expired-pkg", "1.0.0").Return(nil)
 			},
 			fetchFunc: func(ctx context.Context) (io.ReadCloser, string, error) {
 				return io.NopCloser(strings.NewReader("refreshed data")), "https://registry.npmjs.org/expired-pkg", nil
@@ -435,6 +437,7 @@ func TestGet(t *testing.T) {
 				m.On("SavePackage", mock.Anything, mock.Anything).Return(nil)
 				// Second Get succeeds (after re-storing)
 				s.On("Get", mock.Anything, "npm/inconsistent/1.0.0").Return(io.NopCloser(strings.NewReader("recovered data")), nil).Once()
+				m.On("UpdateDownloadCount", mock.Anything, "npm", "inconsistent", "1.0.0").Return(nil)
 			},
 			fetchFunc: func(ctx context.Context) (io.ReadCloser, string, error) {
 				return io.NopCloser(strings.NewReader("recovered data")), "https://registry.npmjs.org/inconsistent", nil