chore: cargo fix - remove unused imports

Phase 33-11 Quick Wins - Task 1

- Removed 10 unused imports across JoinIR lowering modules
- Applied via 'cargo fix --allow-dirty'
- No logic changes, only cleanup
- Build: ✅ Success (0 errors, 44 warnings)

Files modified:
- src/mir/join_ir/lowering/generic_case_a/*.rs (5 files)
- src/mir/join_ir/lowering/{if_merge,if_select,loop_patterns,simple_while_minimal}.rs
- src/mir/join_ir_vm_bridge/joinir_function_converter.rs
- src/mir/builder/control_flow/joinir/merge/exit_line/reconnector.rs

src/mir/builder/control_flow/joinir/merge/exit_line/reconnector.rs

@@ -8,7 +8,6 @@
 use crate::mir::builder::joinir_id_remapper::JoinIrIdRemapper;
 use crate::mir::builder::MirBuilder;
 use crate::mir::join_ir::lowering::inline_boundary::JoinInlineBoundary;
-use crate::mir::ValueId;
 
 /// ExitLineReconnector: A Box that manages exit value reconnection
 ///