fix(packaging): tag core wheels per-version instead of abi3

[cyx-6]

Fixes the mainline-only CI, failing on every push to main since #593. Two one-line changes in pyproject.toml:

1. Wheel tag — #593 moved core off abi3 to the per-version C API (WITH_SOABI) but left wheel.py-api = "cp312", so wheels were still tagged cp312-abi3. abi3audit --strict rejected them (27 non-limited-API symbols). Dropped the stale setting so wheels tag per-version.

2. cp313 aarch64 test — with the audit fixed, the test phase ran and hit a second issue: torch ships no cp313 aarch64 wheel for manylinux2014 (manylinux_2_17), so its test install is unsatisfiable. Added cp313-*aarch64 to test-skip (cp313 x86_64 and cp313 aarch64 on manylinux_2_28 still tested).

Verified green across the full mainline-only wheel matrix (all 6 build jobs + clang-tidy) via a temporary PR trigger, now removed.

[gemini-code-assist]

Code Review

This pull request updates pyproject.toml by removing the wheel.py-api = "cp312" configuration and adding a comment explaining that wheels must be tagged per-version (e.g., cp312-cp312) rather than using the limited API (abi3), as the core extension builds against the full per-version Python C API. There are no review comments, and I have no feedback to provide.

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