perf: optimize 1MB limit test performance

Reduce test execution from ~6s to ~1.3s by using efficient
pre-calculation instead of incremental JSON building

Author: jdalton

test/package-url-json-security.test.mts

@@ -45,29 +45,39 @@ describe('PackageURL.fromJSON security features', () => {
     })
 
     it('should handle JSON exactly at 1MB limit', () => {
-      // Create a JSON string that's as close to 1MB as possible without going over
+      // Create a JSON string that's exactly at the 1MB limit much more efficiently
       const targetSize = 1024 * 1024
-      const baseJson = { type: 'npm', name: 'test', qualifiers: {} as any }
 
-      // Build up qualifiers until we're close to the limit
-      let currentJson = JSON.stringify(baseJson)
-      let i = 0
+      // Calculate size of base JSON structure
+      const baseStructure = '{"type":"npm","name":"test","qualifiers":{'
+      const endStructure = '}}'
+      const baseSize = baseStructure.length + endStructure.length
 
-      while (currentJson.length < targetSize - 1000) {
-        baseJson.qualifiers[`q${i}`] = 'x'.repeat(100)
-        currentJson = JSON.stringify(baseJson)
-        i++
-      }
+      // Calculate size needed for qualifiers
+      // Leave some buffer for JSON overhead
+      const remainingSize = targetSize - baseSize - 100
 
-      // Fine-tune to get as close as possible without exceeding
-      while (currentJson.length < targetSize - 10) {
-        baseJson.qualifiers[`final${i}`] = 'x'
-        currentJson = JSON.stringify(baseJson)
+      // Create one large qualifier that takes up most of the space
+      const largeValue = 'x'.repeat(Math.floor(remainingSize * 0.95))
+      const qualifiers: Record<string, string> = { bigQualifier: largeValue }
+
+      // Add a few smaller qualifiers to fine-tune the size
+      let currentSize = baseStructure.length + JSON.stringify(qualifiers).length - 1 + endStructure.length
+      let i = 0
+      while (currentSize < targetSize - 50) {
+        qualifiers[`q${i}`] = 'x'.repeat(10)
+        currentSize = baseStructure.length + JSON.stringify(qualifiers).length - 1 + endStructure.length
         i++
       }
 
-      const finalJson = currentJson
+      const finalJson = JSON.stringify({
+        type: 'npm',
+        name: 'test',
+        qualifiers
+      })
+
       expect(finalJson.length).toBeLessThanOrEqual(targetSize)
+      expect(finalJson.length).toBeGreaterThan(targetSize - 1000)
 
       // Should work when under the limit
       const result = PackageURL.fromJSON(finalJson)