fix: [IPv6 Port Service] IPv6 address validation rules need review for accepted address ranges

[PeterJhongLinksys]

Description

The IPv6 address validation on the IPv6 Port Service page may be overly restrictive or have gaps. The current rules need review to ensure the accepted address ranges match the actual product requirements.

Current Validation

The service (lib/page/ipv6_port_service/services/usp_ipv6_port_service_service.dart:167) applies two validation layers:

1. IPv6Rule (lib/validator_rules/rules.dart:161) — basic format check using regex + Uri.parseIPv6Address()
2. IPv6WithReservedRule (lib/validator_rules/rules.dart:199) — rejects reserved ranges and only allows Global Unicast addresses (2000::/3, first byte 0x20–0x3F)

Rejected ranges include: loopback (::1), link-local (fe80::/10), multicast (ff00::/8), ULA (fc00::/7), unspecified (::), deprecated 6bone (3ffe::/16), and unallocated (5f00:: to 7fff::).

Expected Behavior

Review and confirm whether the accepted IPv6 address ranges align with the intended use cases for port service rules. Adjust validation if certain address types should be permitted.

[PeterJhongLinksys]

[Root Cause]
IPv6WithReservedRule only allowed Global Unicast addresses (2000::/3) and rejected link-local (fe80::/10) and ULA (fc00::/7). Since LAN devices commonly use link-local addresses (e.g. fe80::1862:0c99:2c88:ac12), users selecting a device from the autocomplete list would get a validation error.

[Solution]
Updated IPv6WithReservedRule to accept link-local (fe80::/10) and ULA (fc00::/7) in addition to Global Unicast (2000::/3). Still rejects loopback (::1), multicast (ff00::/8), unspecified (::), and deprecated 6bone (3ffe::/16). Updated corresponding tests.

Commit: f56d47c