Prepare v0.4 release and open source docs

Tests/IHatePDFsCoreTests/PerformanceBudgetTests.swift

@@ -0,0 +1,46 @@
+import AppKit
+import PDFKit
+import XCTest
+@testable import IHatePDFsCore
+
+final class PerformanceBudgetTests: XCTestCase {
+    func testLargeDocumentFullAnnotationSnapshotPerformance() {
+        let document = makeLargeAnnotatedDocument(pageCount: 500, annotationEvery: 10)
+
+        measure {
+            let snapshots = AnnotationReader.snapshots(in: document)
+            XCTAssertEqual(snapshots.count, 50)
+        }
+    }
+
+    func testLargeDocumentPageScopedAnnotationRefreshPerformance() throws {
+        let document = makeLargeAnnotatedDocument(pageCount: 500, annotationEvery: 10)
+        let targetPage = try XCTUnwrap(document.page(at: 250))
+
+        measure {
+            let snapshots = AnnotationReader.snapshots(in: document, pages: [targetPage])
+            XCTAssertEqual(snapshots.count, 1)
+            XCTAssertEqual(snapshots.first?.pageIndex, 250)
+        }
+    }
+
+    private func makeLargeAnnotatedDocument(pageCount: Int, annotationEvery stride: Int) -> PDFDocument {
+        let document = PDFDocument()
+
+        for pageIndex in 0..<pageCount {
+            let page = PDFPage()
+            document.insert(page, at: pageIndex)
+
+            guard pageIndex.isMultiple(of: stride) else { continue }
+            let insertion = AnnotationFactory.noteInsertion(
+                on: page,
+                near: CGPoint(x: 120, y: 160),
+                comment: "Note on page \(pageIndex + 1)",
+                author: "Professor"
+            )
+            page.addAnnotation(insertion.annotation)
+        }
+
+        return document
+    }
+}