test: replace Go tests with YAML test cases for PURL builtins

- Remove v1/topdown/purl_test.go
- Add YAML test cases for purl.is_valid and purl.parse
- Include tests for valid/invalid PURLs and error cases
- Set strict_error flag for parse error test to ensure proper error propagation

Author: Anivar A Aravind

v1/test/cases/testdata/v1/purlbuiltins/test-purl-is-valid.yaml

@@ -0,0 +1,45 @@
+---
+cases:
+  - note: purlbuiltins/is_valid_npm
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.is_valid("pkg:npm/[email protected]", x)
+        }
+    want_result:
+      - x: true
+
+  - note: purlbuiltins/is_valid_maven
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.is_valid("pkg:maven/org.apache.xmlgraphics/[email protected]", x)
+        }
+    want_result:
+      - x: true
+
+  - note: purlbuiltins/is_valid_invalid
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.is_valid("not-a-purl", x)
+        }
+    want_result:
+      - x: false
+
+  - note: purlbuiltins/is_valid_empty
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.is_valid("", x)
+        }
+    want_result:
+      - x: false

v1/test/cases/testdata/v1/purlbuiltins/test-purl-parse.yaml

@@ -0,0 +1,88 @@
+---
+cases:
+  - note: purlbuiltins/parse_simple
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("pkg:npm/[email protected]", x)
+        }
+    want_result:
+      - x:
+          type: "npm"
+          name: "foobar"
+          version: "12.3.1"
+
+  - note: purlbuiltins/parse_with_namespace
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("pkg:maven/org.apache.xmlgraphics/[email protected]", x)
+        }
+    want_result:
+      - x:
+          type: "maven"
+          namespace: "org.apache.xmlgraphics"
+          name: "batik-anim"
+          version: "1.9.1"
+
+  - note: purlbuiltins/parse_with_qualifiers
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("pkg:rpm/fedora/[email protected]?arch=i386&distro=fedora-25", x)
+        }
+    want_result:
+      - x:
+          type: "rpm"
+          namespace: "fedora"
+          name: "curl"
+          version: "7.50.3-1.fc25"
+          qualifiers:
+            arch: "i386"
+            distro: "fedora-25"
+
+  - note: purlbuiltins/parse_with_subpath
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("pkg:github/owner/[email protected]#path/to/file.js", x)
+        }
+    want_result:
+      - x:
+          type: "github"
+          namespace: "owner"
+          name: "repo"
+          version: "v1.0.0"
+          subpath: "path/to/file.js"
+
+  - note: purlbuiltins/parse_minimal
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("pkg:npm/lodash", x)
+        }
+    want_result:
+      - x:
+          type: "npm"
+          name: "lodash"
+
+  - note: purlbuiltins/parse_invalid
+    query: data.generated.p = x
+    modules:
+      - |
+        package generated
+        p := x if {
+          purl.parse("not-a-purl", x)
+        }
+    want_error: 'purl.parse: invalid PURL'
+    strict_error: true