Implement watching a path

Each inotify instance produces events for paths in its watch list. Each
item in the watch list is identified by its watch descriptor. Different
paths can be watched for different events.

Tests/InotifyIntegrationTests/Utilities.swift

@@ -0,0 +1,10 @@
+import Foundation
+
+func withTempDir(_ body: (String) async throws -> Void) async throws {
+	let dir = FileManager.default.temporaryDirectory
+		.appendingPathComponent("InotifyIntegrationTests-\(UUID().uuidString)")
+		.path
+	try FileManager.default.createDirectory(atPath: dir, withIntermediateDirectories: true)
+	defer { try? FileManager.default.removeItem(atPath: dir) }
+	try await body(dir)
+}

Tests/InotifyIntegrationTests/WatchTests.swift

@@ -0,0 +1,21 @@
+import Testing
+import Foundation
+@testable import Inotify
+
+@Suite("Watch Management")
+struct WatchTests {
+	@Test func addWatchReturnsValidDescriptor() async throws {
+		try await withTempDir { dir in
+			let watcher = try Inotify()
+			let wd = try await watcher.addWatch(path: dir, mask: .allEvents)
+			#expect(wd >= 0)
+		}
+	}
+
+	@Test func addWatchOnInvalidPathThrows() async throws {
+		let watcher = try Inotify()
+		await #expect(throws: InotifyError.self) {
+			try await watcher.addWatch(path: "/nonexistent-\(UUID())", mask: .allEvents)
+		}
+	}
+}