UICR: End address might be misscalculated if start page is not 0

[microbit-carlos]

microbit-fs/src/uicr.ts

Lines 200 to 208 in 9738a5b

	return {
	flashPageSize: pageSize,
	runtimeStartPage: startPage,
	runtimeStartAddress: startPage * pageSize,
	runtimeEndUsed: pagesUsed,
	runtimeEndAddress: pagesUsed * pageSize,
	versionAddress,
	version,
	};

Will need to check that runtimeEndUsed represents numbers of pages used from the start page: https://microbit-micropython.readthedocs.io/en/latest/devguide/hexformat.html#uicr-format

Then update the code and add more tests.