fix(nix): bump Python 3.11 → 3.12 to resolve sphinx 9.1.0 build failure

[lopezpalacios]

Problem

nix build fails on current main with:

error: sphinx-9.1.0 not supported for interpreter python3.11

Sphinx 9.1.0 (pulled transitively via pyproject-build-systems) dropped Python 3.11 support.

Fix

Bump nix/python.nix from python311 → python312. The project's pyproject.toml requires >=3.11, so 3.12 is fully compatible.

Tested

• nix build succeeds on aarch64-darwin (M2 Max, macOS)
• hermes setup, hermes doctor, and hermes chat all work correctly
• hermes doctor confirms Python 3.12.13

[alt-glitch]

Likely duplicate of #12208 (merged) — same Python 3.11→3.12 bump in nix/python.nix. That fix is already on main.

[alt-glitch]

Likely duplicate of #12208 (merged).

[teknium1]

Thanks for the contribution @lopezpalacios! This fix has already landed on main via a prior commit.

Automated hermes-sweeper review found:

• nix/python.nix on main already uses python312 throughout (function signature, all mkPrebuiltOverride calls, and pythonSet definition)
• Commit b0efdf37d — "fix(nix): upgrade Python 3.11 → 3.12, add cross-platform eval check (fix(nix): upgrade Python 3.11 → 3.12 and add cross-platform eval check #12208)" — merged the same fix before this PR was opened

The sphinx 9.1.0 / Python 3.11 incompatibility you identified is a real issue and you found the right fix — it just got addressed independently. Closing as already implemented.