🧹 Replace unsafe unwrap with proper error handling in thumb_lower

[undivisible]

🎯 What:
Replaced the unwrap() call at in-cli/src/native_emit/thumb_lower.rs:115 with proper error handling using .ok_or_else() and the ? operator.

💡 Why:
The previous code would unconditionally panic (unwrap) if the target entry offset was not found in the offsets map during lowering. Replacing this with an explicit error return gracefully propagates the failure back through the Result chain to the caller, preventing compiler crashes on malformed inputs (like empty extern functions) and improving the overall maintainability and safety of the pass.

✅ Verification:

• Linting & Formatting: Ran cargo fmt and cargo clippy --all-targets --features extended --locked -- -D warnings within the in-cli crate (no warnings).
• Unit Testing: Ran cargo test -p inauguration native_emit and the full cargo test -p inauguration suite; all tests passed successfully.
• Integration Testing: Executed the full conformance suite (IN_TEST_SKIP_SWIFT=1 ./install.sh && ~/.local/bin/in test), which completed successfully (accounting for known pre-existing baseline failures that were not regressions).
• Code Review: Requested and passed automated code review with a "Correct" rating.

✨ Result:
The lower_module function now correctly returns a detailed Err instead of panicking when an entry offset is missing, making the Thumb-2 backend more robust without changing any valid lowering behavior.

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PR created automatically by Jules for task 4335764489212883950 started by @undivisible

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Note

Low Risk
Single-site error-handling change in the Thumb lowerer; no behavior change for successfully lowered modules, only replaces a panic with a propagated Result error.

Overview
lower_module in the Thumb-2 backend no longer panics when the chosen entry symbol has no emitted code offset (e.g. an extern with an empty body, which is skipped during emission and never added to offsets).

The final entry_offset lookup replaces unwrap() with ok_or_else + ?, returning a clear Err message instead of aborting the compiler. Valid entries with real bodies are unchanged.

^{Reviewed by Cursor Bugbot for commit 4bf73b3. Configure here.}

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