Guard get_ipython() being Optional (fixes mypy on master)

[emeryberger]

The linters workflow is failing on master, independently of any PR.

IPython 9.16 annotates get_ipython() as returning Optional[InteractiveShell], and history_manager is itself optional. mypy 2.3 therefore reports four union-attr errors in scalene_tracing.py:157 and scalene_magics.py:43. The existing # type: ignore[no-untyped-call, unused-ignore] on those lines doesn't cover that error code — mypy says so explicitly:

scalene/scalene_tracing.py:157: error: Item "None" of "InteractiveShell | None" has no attribute "history_manager"  [union-attr]
scalene/scalene_tracing.py:157: note: Error code "union-attr" not covered by "type: ignore[no-untyped-call, unused-ignore]" comment
scalene/scalene_tracing.py:157: error: Item "None" of "Any | None" has no attribute "input_hist_raw"  [union-attr]
scalene/scalene_magics.py:43: error: Item "None" of "InteractiveShell | None" has no attribute "history_manager"  [union-attr]
scalene/scalene_magics.py:43: note: Error code "union-attr" not covered by "type: ignore[no-untyped-call, unused-ignore]" comment
scalene/scalene_magics.py:43: error: Item "None" of "Any | None" has no attribute "input_hist_raw"  [union-attr]
Found 4 errors in 2 files (checked 66 source files)

No commit caused this. Master's last linters run was 2026-07-05 and passed, and nothing has landed since — it broke on its own when CI's unpinned pip install mypy ruff types-PyYAML pydantic started resolving newer versions. Confirmed by dispatching the workflow against unmodified master: run 30640136643 fails with the identical four errors.

Fix

Guard both levels — the shell and its history manager:

• _handle_jupyter_cell() returns False without a live shell, falling through to the ordinary filename rules. That's the behavior it already had when the cell regex didn't match.
• run_code() prints a plain message and returns. Neither value can really be None there — a magic only runs inside a live shell — so this exists to satisfy the type checker without an AttributeError as the fallback.

The # type: ignore comments stay: on older IPython get_ipython() is untyped, so no-untyped-call still applies, and unused-ignore keeps the comment valid once it no longer does.

Verification

• Reproduced in a venv pinned to CI's exact versions (mypy 2.3.0, IPython 9.16.0): 4 errors before, Success: no issues found in 66 source files after. ruff check scalene clean.
• Re-checked against the older pair (mypy 1.19.0, IPython 9.9.0) so the fix holds in both directions — no new errors; only the unrelated, pre-existing scalene_signal_manager.py:314 one that mypy 2.3 doesn't flag.
• Behavior spot-checked for all three shapes: live shell (recovers the cell contents, writes the file, returns True), get_ipython() returning None, and history_manager being None — the last two return cleanly instead of raising.
• Full pytest suite: 442 passed, 13 skipped.

Found while checking CI on #1087, which is blocked by this same failure.

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