ZMQ sub *:port failed randomly in CI

[pancak3]

What happened:
KV cache test failed sometimes; ZQM tries to sub but the address is in use. It happens in CI.

See jobs:
https://github.com/llm-d/llm-d-inference-sim/actions/runs/17185865922/job/48754776272#step:8:131
https://github.com/llm-d/llm-d-inference-sim/actions/runs/17186323665/job/48755883796

Line:

llm-d-inference-sim/pkg/kv-cache/kv_cache_test.go

Line 39 in bdc5ecb

subEndpoint = "tcp://*:5557"

Guess:
The executor that runs the job has side process occupied the addr *:5557
The addr is not "fully" released

Proposal:
@pancak3 - use 127.0.0.1 in tests for both sub and pub
@irar2 - look for available port

What you expected to happen:
Pass, successfully sub the addr

How to reproduce it (as minimally and precisely as possible):
Run test, it occasionally fails

Anything else we need to know?:
N/A

Environment:
N/A