Ensure that XML property lists contain exactly one root value inside the <plist> element and reject any additional value nodes before </plist>.

Add tests covering root value handling and nested CF$UID conversion behavior.

Co-authored-by: Sami Kortelainen <sami.kortelainen@piceasoft.com>
Co-authored-by: Nikias Bassen <nikias@gmx.li>

This change adds stricter validation for numeric and date nodes,
including full-input consumption, overflow/range checks, and rejection
of invalid floating-point values. Whitespace handling is clarified by
explicitly trimming trailing XML whitespace for value nodes.

Otherwise test fail with error [: -neq: binary operator expected

Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>

Without the change tests ran in parallel occasionally clobber outputs of
one another and fail as:

    $ make check -j16 VERBOSE=y
    ...
    FAIL: huge
    ==========
    Converting
    File ../test/data/5.plist is open
    PList XML parsing succeeded
    PList BIN writing succeeded
    PList BIN parsing succeeded
    PList XML writing succeeded
    Size of input and output is different
    Input size : 4292380
    Output size : 4305301
    Comparing
    PList parsing failed
    FAIL huge.test (exit status: 3)

Closes: https://github.com/libimobiledevice/libplist/issues/234#issuecomment-1743820556

plist_read_from_file() is a convenience function that will open a
given file, checks its size, allocates a buffer large enough to
hold the full contents, and reads from file to fill the buffer.
Then, it calls plist_from_memory() to convert the data to plist
format.
A (breaking) change had to be made so that plist_from_memory() will
also return the parsed format in its 4th argument (if non-NULL).

This makes the code more readable. Obviously all the code that uses it
is also updated.