fix(eliminate): skip inlining when substitution site is inside a loop body

[NikolaRHristov]

Problem

A binding used only inside a for/while/loop body has RefCount=1 and passes every existing check, so it gets inlined. The initialiser is then placed inside the loop and runs on every iteration instead of once. For side-effecting or expensive initialisers this changes observable behaviour. For move-only types it causes E0382 on the second iteration.

// before - initialiser runs once
let X = expensive();
for item in &collection { process(item, X); }

// after eliminate (wrong) - initialiser runs N times
for item in &collection { process(item, expensive()); }

Fix

Count.rs

CountReferences now returns (usize, bool, bool): the third value is InLoop.

ExprCounter gains an InsideLoop: bool context flag and overrides visit_expr_for_loop, visit_expr_while, and visit_expr_loop to set it before descending. Any reference to Target found while InsideLoop is true sets InLoop = true on the counter.

The flag is saved and restored around each loop variant so nested loops compose correctly.

Inline.rs

EliminateBlock destructures the new three-tuple and adds || InLoop to the skip condition alongside InClosure.

Tests added

• Count::Tests::LoopBodySetsInLoop - for loop sets InLoop
• Count::Tests::WhileBodySetsInLoop - while loop sets InLoop
• Count::Tests::LoopExprBodySetsInLoop - bare loop sets InLoop
• Count::Tests::OutsideLoopNotFlagged - usage outside loop leaves InLoop false
• Count::Tests::UsedInsideAndOutsideLoop - mixed: count=2 and InLoop=true
• Inline::Tests::LoopBodyBindingKept - for loop integration
• Inline::Tests::WhileBodyBindingKept - while loop integration
• Inline::Tests::LoopExprBindingKept - bare loop integration
• Inline::Tests::OutsideLoopStillInlined - no regression for normal inline