Fix double-decode on presigm param

This was only passing the tests because we incorrecly were double-encoding the presigned params too.

src/lambda-handler.ts

@@ -33,7 +33,7 @@ const streamify_handler: StreamifyHandler = async ( event, response ) => {
 	// If there is a presign param, we need to decode it and add it to the args. This is to provide a secondary way to pass pre-sign params,
 	// as using them in a Lambda function URL invocation will trigger a Lambda error.
 	if ( args.presign ) {
-		const presignArgs = new URLSearchParams( decodeURIComponent( args.presign ) );
+		const presignArgs = new URLSearchParams( args.presign );
 		for ( const [ key, value ] of presignArgs.entries() ) {
 			args[ key as keyof Args ] = value;
 		}

tests/test-private-upload.ts

@@ -95,7 +95,7 @@ test( 'Test get private upload with presign params', async () => {
 		'headers': {
 		},
 		'queryStringParameters': {
-			presign: encodeURIComponent( new URLSearchParams( presignParams ).toString() ),
+			presign: new URLSearchParams( presignParams ).toString(),
 		},
 		'isBase64Encoded': false,
 	};