Add test to verify mount() correctly handles files (addresses #503)

This test confirms that the mount() method properly creates a file node
(not a directory) when mounting a file. The issue described in #503
appears to have been resolved in PR #2338 when file mounting support
was added to NODEFS.

The test explicitly checks:
- That the mount point doesn't exist before mounting
- That after mounting a file, isFile() returns true
- That after mounting a file, isDir() returns false

This ensures the behavior described in issue #503 is working correctly.

Author: jnealey88

packages/php-wasm/node/src/test/mount.spec.ts

@@ -138,6 +138,21 @@ describe('Mounting', () => {
 				}
 			});
 
+			it('Should create a file node, not a directory, when mounting a file', async () => {
+				// This test addresses issue #503
+				// Ensure the mount point doesn't exist yet
+				expect(php.fileExists(fileMountPoint)).toBe(false);
+
+				await php.mount(
+					fileMountPoint,
+					createNodeFsMountHandler(filePath)
+				);
+
+				// The mount point should be a file, not a directory
+				expect(php.isFile(fileMountPoint)).toBe(true);
+				expect(php.isDir(fileMountPoint)).toBe(false);
+			});
+
 			it('Should unmount mounted file and remove created node from VFS', async () => {
 				const unmount = await php.mount(
 					fileMountPoint,