cutils: Adjust signature of parse_uint[_full]

It's already confusing that we have two very similar functions for
wrapping the parse of a 64-bit unsigned value, differing mainly on
whether they permit leading '-'.  Adjust the signature of parse_uint()
and parse_uint_full() to be like all of qemu_strto*(): put the result
parameter last, use the same types (uint64_t and unsigned long long
have the same width, but are not always the same type), and mark
endptr const (this latter change only affects the rare caller of
parse_uint).  Adjust all callers in the tree.

While at it, note that since cutils.c already includes:

    QEMU_BUILD_BUG_ON(sizeof(int64_t) != sizeof(long long));

we are guaranteed that the result of parse_uint* cannot exceed
UINT64_MAX (or the build would have failed), so we can drop
pre-existing dead comparisons in opts-visitor.c that were never false.

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230522190441.64278-8-eblake@redhat.com>
[eblake: Drop dead code spotted by Markus]
Signed-off-by: Eric Blake <eblake@redhat.com>

blockdev.c

@@ -341,10 +341,10 @@ static bool parse_stats_intervals(BlockAcctStats *stats, QList *intervals,
         switch (qobject_type(entry->value)) {
 
         case QTYPE_QSTRING: {
-            unsigned long long length;
+            uint64_t length;
             const char *str = qstring_get_str(qobject_to(QString,
                                                          entry->value));
-            if (parse_uint_full(str, &length, 10) == 0 &&
+            if (parse_uint_full(str, 10, &length) == 0 &&
                 length > 0 && length <= UINT_MAX) {
                 block_acct_add_interval(stats, (unsigned) length);
             } else {