docs(test): add fileoverview headers to core and type-specific test files

Add descriptive @fileoverview headers to core functionality tests:
- package-url.test.mts: main PackageURL API, constructor, parsing, encoding
- purl-types.test.mts: type-specific normalizations (npm, pub, pypi)

Author: jdalton

test/package-url.test.mts

@@ -20,6 +20,12 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+/**
+ * @fileoverview Core unit tests for PackageURL class.
+ * Tests the main PackageURL API including constructor validation, toString/fromString parsing,
+ * encoding/decoding, qualifiers, subpaths, known qualifier names immutability, input validation,
+ * and support for parsing without the "pkg:" prefix for improved developer ergonomics.
+ */
 import { describe, expect, it } from 'vitest'
 
 import { PackageURL } from '../src/package-url.js'

test/purl-types.test.mts

@@ -20,6 +20,11 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+/**
+ * @fileoverview Unit tests for type-specific PackageURL behavior.
+ * Tests package-type-specific normalizations and validations for npm (legacy names, builtins),
+ * pub (dash-to-underscore), and pypi (lowercase, underscore-to-dash) package types.
+ */
 import { describe, expect, it } from 'vitest'
 
 import npmBuiltinNames from '../data/npm/builtin-names.json'