🧹 Refactor overly long lower_expr function in lower_core.rs

[undivisible]

🎯 What:
The lower_expr function in in-cli/src/lower_core.rs was overly long (exceeding 150 lines), serving as a monolithic dispatch and implementation function for lowering core IR expressions into textual SIL. This PR extracts the specific logic for each Expr variant into distinct, well-named helper functions (e.g., lower_int_lit, lower_binary, lower_call), leaving lower_expr as a clean, purely delegating match statement.

💡 Why:
Breaking up the massive lower_expr function drastically improves readability and maintainability. It isolates the state and control flow required for lowering individual AST nodes, reducing the cognitive load required to understand or modify specific expression lowerings in the future.

✅ Verification:

• Verified the exact logic was preserved by strictly extracting without behavior changes.
• Executed cd in-cli && cargo check successfully.
• Executed cd in-cli && cargo test successfully, proving no regressions.
• Verified code health and style via cd in-cli && cargo clippy --all-targets --features extended --locked -- -D warnings and cargo fmt.

✨ Result:
The lower_expr function is now extremely concise and readable, and the implementation details for lowering specific expression variants are properly encapsulated in targeted helper functions, significantly boosting the codebase's long-term maintainability.

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PR created automatically by Jules for task 17815256096972707046 started by @undivisible

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Note

Low Risk
Mechanical extraction in the compiler lowering path with tests reported passing; risk is limited to accidental copy-paste divergence, not new features or security surface.

Overview
Refactors the monolithic lower_expr in lower_core.rs by splitting each Expr lowering path into dedicated helpers (lower_int_lit, lower_ident, lower_unary, lower_binary, lower_struct_init, lower_call, etc.).

lower_expr is now a thin match that delegates to those functions; constant folding in unary/binary lowering reuses the new literal helpers instead of inlining SSA emission. No intended change to emitted SIL—structure and readability only.

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