fix(compiler): diagnose optional binary operands

[chess10kp]

Summary

• diagnose un-narrowed optional operands before binary numeric promotion and magic-method resolution
• preserve direct equality and union-annotation handling
• cover forward and reflected arithmetic with the existing native optional diagnostics fixture

Reproduction

Before this change, jac check --native-coverage accepted return x + 1 for x: int | None without an optional-operand diagnostic. The attribute-access twin still reported its existing optional error.

Verification

• jac check --native-coverage /tmp/jac-8547-repro.jac reports E1121 for x + 1
• native fixture compilation reports E1121 for both x + 1 and 1 + x
• the one targeted test-file run was blocked before tests by the installed 0.36.1 launcher rejecting pre-existing ctypes type signatures in the current test file

Closes #8547

[christianwilkins]

Reviewed head bf3abd00ce57b7ca21ca9b705d0643420b67bfd2, including the arithmetic diagnostic, the follow-up loop guards, the native fixtures, the optional-diagnostic helper, and the binary-operation dispatch around the new guard.

P2: runtime bitwise OR bypasses the new optional-operand check. With x: int | None, both x | 1 and 1 | x still produce no optional diagnostic. The union-annotation path already returns above this guard; exempting every BW_OR also exempts runtime operands. Please cover both directions and narrow the exemption to actual annotations.

Local validation: a direct JacProgram.compile probe with CompileOptions(force_codespace="native", force_target_program=True) produced E1121 for forward addition, reflected addition, and bitwise AND, but neither OR expression. Its assertion expecting all five diagnostics failed (3 reported); guarded addition and optional equality produced no errors. An initial test-helper import hit the existing ctypes-signature checking obstacle described in the PR. A separate temporary-change control did not finish compilation and is not counted as validation; the source was restored and the worktree is clean.

Current-head CI is green (25 successful checks, 3 skipped), but GitHub reports merge conflicts. Changes requested: fix and test runtime OR, resolve the conflicts while preserving the follow-up narrowing guards, and rerun validation/CI on the resulting head. Maintainer review/merge follows after those author actions.

[christianwilkins]

[P2] Do not exempt runtime bitwise OR from the optional-operand diagnostic. The annotation-only OR case already returns at lines 354–363. Here, x | 1 and 1 | x with x: int | None skip the guard and still emit no E1121. A forced-native compile of those cases alongside x + 1, 1 + x, and x & 1 reports only the latter three errors. Limit the exemption to actual union annotations and add both runtime OR directions to the regression fixture.