Fix skip_fhrp_group_ips unbinding all interface IPs and py<3.12 import (continues #476)

[semx]

Builds on #476 by @Noah418 / @afoster (their commits are included here) and drives the v1.9.0 milestone item to a working state. Two fixes on top of their work, plus the first unit tests in the repo.

1. Import broken on Python < 3.12

The FHRP log line used an f-string with nested double quotes:

f"Ip address {grab(ip, "data.address")} ..."

That syntax is only valid from Python 3.12 (PEP 701). The project supports Python 3.6+, so on 3.6–3.11 the module fails to import with SyntaxError: f-string: unmatched '(' — exactly what @ionoci reported. Reproduced on 3.11; fixed with single quotes inside; verified the module imports again on 3.11.

2. skip_fhrp_group_ips unbound every interface IP

@ionoci also reported that enabling skip_fhrp_group_ips left all VM interface IPs unbound. The FHRP check ran inside the address-matching loop before the candidate address was compared to the IP being processed, so any FHRP-group IP anywhere in the inventory raised skip_this_ip, and the if skip_this_ip: continue downstream dropped the IP being handled. The effect depended on inventory order and ignored the VRF.

The fix moves the check to a dedicated pass before the matching loop that looks for an FHRP-group assignment on this exact address in the same VRF. An unrelated FHRP IP can no longer suppress a regular IP, the outcome no longer depends on inventory order, and the #445 behaviour (not rebinding a real FHRP-group IP) is preserved.

Tests

First unit tests in the repository (tests/test_fhrp_ip_binding.py), running against the real add_update_interface path via the in-memory NetBoxInventory — no live NetBox or vCenter needed:

• regular IP stays bound when an unrelated FHRP IP is present, in both inventory orders (parametrized);
• a matching FHRP-group IP is not reassigned (the Sync overwrites FHRPGroup assignement #445 feature);
• FHRP match is scoped to the same VRF;
• control case with the flag disabled.

Verified empirically: the regression and VRF tests fail on the original loop logic and all pass with the fix, on Python 3.11 and 3.13.

Closes #445.