Fix #2 - Reject IP addresses that Moodle cannot match

The custom IP field and the predefined ranges form accepted invalid
entries such as 2001:db8::1garbage, 192.168.1.0/24garbage or
192.168.1.0/999. address_in_subnet() silently skips those entries, so a
"must not" restriction with a typo let blocked users in.

Validation now only accepts formats address_in_subnet() can match: a
single address, a subnet (mask 0-32 / 0-128) or a range in the last
group with end >= start. IPv6 forms cleanremoteaddr() cannot parse are
rejected as well. JS and PHP share the same rules; PHP also checks each
entry against address_in_subnet() as a safety net.

- Allow spaces after commas in the restriction field
- Support IPv6 ranges, e.g. 2001:db8::1-ff
- Add PHPUnit tests for helper::is_valid_ipaddress_list()
- Bump version to 2026101500 (5.3.2)

version.php

@@ -27,8 +27,8 @@
 defined('MOODLE_INTERNAL') || die();
 
 $plugin->component = 'availability_ipaddress';
-$plugin->version = 2026101400;
-$plugin->release = '5.3.1';
+$plugin->version = 2026101500;
+$plugin->release = '5.3.2';
 $plugin->requires = 2016120500;
 $plugin->maturity = MATURITY_STABLE;
 $plugin->supported = [400, 503];