[LifetimeSafety] Add script for performance benchmarking (#147315)

This patch introduces a new Python-based benchmarking tool for Clang's Lifetime Safety analysis. This script automates the process of generating targeted C++ test cases, measuring the performance of the analysis, and determining its empirical computational complexity.

The tool helps track and validate the performance of the dataflow analysis, ensuring that future optimizations have a measurable impact and that the analysis scales efficiently.

Components:

* **Generate**: Creates pathological C++ test cases with specific patterns (pointer cycles and CFG merges) designed to stress-test the analysis.

* **Compile & Trace**: Compiles the generated code using `-ftime-trace`.

* **Analyze & Report**: Performs a curve-fit on the timing data to determine the empirical complexity ( **O(n<sup>k</sup>)**) and outputs a markdown report.

---

**Usage**:
<details>
  <summary>ninja benchmark_lifetime_safety_analysis</summary>

[12/13] Running Lifetime Analysis performance benchmarks...
Benchmark files will be saved in: <BUILD_DIR_REDACTED>/tools/clang/test/Analysis/LifetimeSafety/benchmark_results

Running performance benchmarks...
--- Running Test: Cycle with N=10 ---
    Total: 10.11 ms | Analysis: 2.70 ms
--- Running Test: Cycle with N=25 ---
    Total: 61.51 ms | Analysis: 53.05 ms
--- Running Test: Cycle with N=50 ---
    Total: 688.56 ms | Analysis: 677.32 ms
--- Running Test: Cycle with N=75 ---
    Total: 3.09 s | Analysis: 3.07 s
--- Running Test: Cycle with N=100 ---
    Total: 9.31 s | Analysis: 9.30 s
--- Running Test: Cycle with N=150 ---
    Total: 44.92 s | Analysis: 44.91 s
--- Running Test: Merge with N=10 ---
    Total: 8.54 ms | Analysis: 0.00 ms
--- Running Test: Merge with N=50 ---
    Total: 38.79 ms | Analysis: 27.13 ms
--- Running Test: Merge with N=100 ---
    Total: 219.45 ms | Analysis: 205.20 ms
--- Running Test: Merge with N=200 ---
    Total: 1.67 s | Analysis: 1.65 s
--- Running Test: Merge with N=400 ---
    Total: 12.57 s | Analysis: 12.55 s
--- Running Test: Merge with N=800 ---
    Total: 100.48 s | Analysis: 100.43 s


Generating Markdown Report...
</details>

<details>
  <summary>Sample Report: </summary>

# Lifetime Analysis Performance Report
> Generated on: 2025-07-08 14:18:52 

---

## Test Case: Pointer Cycle in Loop

| N   | Analysis Time | Total Clang Time |
|:----|--------------:|-----------------:|
| 10  |       2.70 ms |         10.11 ms |
| 25  |      53.05 ms |         61.51 ms |
| 50  |     677.32 ms |        688.56 ms |
| 75  |        3.07 s |           3.09 s |
| 100 |        9.30 s |           9.31 s |
| 150 |       44.91 s |          44.92 s |

**Complexity Analysis:**
- The performance for this case scales approx. as **O(n<sup>3.88</sup>)**.
- **95% Confidence interval for exponent:** `[3.86, 3.90]`.

---

## Test Case: CFG Merges

| N   | Analysis Time | Total Clang Time |
|:----|--------------:|-----------------:|
| 10  |       0.00 ms |          8.54 ms |
| 50  |      27.13 ms |         38.79 ms |
| 100 |     205.20 ms |        219.45 ms |
| 200 |        1.65 s |           1.67 s |
| 400 |       12.55 s |          12.57 s |
| 800 |      100.43 s |         100.48 s |

**Complexity Analysis:**
- The performance for this case scales approx. as **O(n<sup>3.00</sup>)**.
- **95% Confidence interval for exponent:** `[2.99, 3.01]`.

---

</details>