test: zero-pad the port in feature_anchors' expected hex #36559

feature_anchors.py builds the expected anchors.dat substring from each peer's port with hex(port)[2:], which is not zero-padded. The port is serialized as two bytes, so for ports below 4096 the expected string is one hex digit short and assert ip_port in anchors_hex fails.

This only shows up with a non-default port range, for example when avoiding local listeners:

TEST_RUNNER_PORT_MIN=1100 test/functional/feature_anchors.py

fails on master with AssertionError at the assert ip_port in anchors_hex line and passes with this change; the default range still passes.

Disclosure: AI (Claude Fable 5.1) was used to find this issue and to draft this PR.

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External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36559
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36559.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36559#author-ralph

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Yep, also here I added the disclosure after reading the policy. Again a fix for a non-default configuration, so ignore if you don't want to review AI-generated code at all.

lightly tested ACK 2f7622e3f6f7ef431a7d5ec522958da62f33cec4

I don't see a problem here, the formatting matches the serialization, the fix seems narrow.

Ok