test(minifier): add comprehensive test coverage for unary plus removal (#12860)

This PR adds comprehensive test coverage for the existing unary plus
removal functionality in `substitute_alternate_syntax.rs`, which safely
removes redundant unary plus operators (`+`) in mathematical operations
while avoiding BigInt compatibility issues.

## Problem

The existing implementation correctly handles safe removal of unary plus
operators, but the test coverage was minimal and didn't demonstrate the
full capability of the feature. This made it unclear what scenarios were
supported.

## Solution

Added comprehensive test cases that demonstrate the implementation
correctly handles:

- **Mathematical operations**: Division, multiplication, bitwise
operations (`|`, `&`, `^`)
- **Complex expressions**: Method calls, member access, nested
expressions
- **Safety checks**: Properly preserves unary plus when operand types
are unknown to avoid BigInt runtime errors

## Examples

```javascript
// ✅ Safe optimizations (other operand is number literal)
+d / 1000          →  d / 1000
1000 * +d          →  1000 * d  
5 | +b             →  5 | b
2 - +x.call()      →  2 - x.call()

// ✅ Correctly preserved (unknown operand types)  
a | +b             →  a | +b  (unchanged)
+a * b             →  +a * b  (unchanged)
```

The expanded test suite confirms the implementation works correctly
across all supported mathematical operations while maintaining BigInt
safety.

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Author: 4 people

crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs

@@ -1689,6 +1689,21 @@ mod test {
         test_same("v = +foo - bar");
         test_same("v = foo - +bar");
         test_same("v = 1 + +foo"); // cannot compress into `1 + foo` because `foo` can be a string
+
+        test("v = +d / 1000", "v = d / 1000");
+        test("v = 1000 * +d", "v = 1000 * d");
+        test("v = +d * 1000", "v = d * 1000");
+        test("v = 2 - +this._x.call(null, node.data)", "v = 2 - this._x.call(null, node.data)");
+
+        test("v = 5 | +b", "v = 5 | b");
+        test("v = +b | 5", "v = b | 5");
+        test("v = 7 & +c", "v = 7 & c");
+        test("v = 3 ^ +d", "v = 3 ^ d");
+        // Don't remove - unsafe for BigInt operations
+        test_same("v = a - +b");
+        test_same("v = +a - b");
+        test_same("v = a | +b");
+        test_same("v = +a | b");
     }
 
     #[test]