tools/nolibc: Add a simple test for writing to a FILE and reading it back

tools/nolibc: Add a simple test for writing to a FILE and reading it back

Add a test that exercises create->write->seek->read to check that using the
stream functions (fwrite() etc) is not totally broken.

The only edge cases this is testing for are:
- Reading the file after writing but without rewinding reads nothing.
- Trying to read more items than the file contains returns the count of
  fully read items.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Link: https://patch.msgid.link/20260105023629.1502801-4-daniel@thingy.jp
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>