fix: capture the return value of array_push in net_addr.cpp

[sagjoshi]

This PR fixes three functions in src/runtime/uv/net_addr.cpp that incorrectly called array_push() without capturing its return value, violating the Lean runtime API contract. When arrays aren't exclusively owned or need reallocation, array_push() returns a new pointer, but the code continued using the old unmodified pointer, resulting in malformed IP addresses with zero-valued octets and failed network connections. The bug was masked in typical usage because arrays were usually exclusively owned with sufficient capacity, causing in-place modification. The fix changes all three functions to capture the return value (ret = array_push(ret, lean_box(octet))), and enhanced tests now validate that all IP address octets are properly populated. DNS resolution now returns correct addresses and all network operations succeed.

Closes #11128

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase f74e21e302bb5eaa372a406649e034ae055988e0 --onto d47b474e41e4b134239ef70fa3c15778cc771bcf. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-10 23:42:57)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase f74e21e302bb5eaa372a406649e034ae055988e0 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-11-10 23:42:58)

[TwoFX]

The bug that this PR is supposed to fix was already fixed by #10854. The tests that this PR adds all pass on recent nightlies, and I don't think that they improve test coverage compared to what we already have, so I'll close this PR.