Add timing measurement for integration tests

[xingzihai]

Summary

This PR addresses issue #985 by adding timing measurement for integration tests.

Changes

• Added TimingResult.cs and TimingRecorder.cs in Cesium.TestFramework to record test timing information
• Modified IntegrationTestRunner.cs to measure time for each test stage:
  • Native compiler compile time
  • Native executable run time
  • Cesium compiler compile time
  • Cesium executable run time
• Timing results are written to a JSON file (integration-test-timing-{OS}-{timestamp}.json) at the end of the test run

Output Format

The JSON file contains:

• Operating system name (Windows/Linux/macOS)
• Timestamp (ISO 8601 format)
• Individual test timing results with:
  • Test name
  • Source file
  • Target architecture (Bit32/Bit64/Wide/Dynamic)
  • Target framework (NetFramework/Net)
  • Native compile time (ms)
  • Native run time (ms)
  • Cesium compile time (ms)
  • Cesium run time (ms)
  • Total test time (ms)
• Summary statistics including totals for each stage

Purpose

This allows CI teams to download the timing results and analyze which stages of the integration tests are taking the most time, helping to identify optimization opportunities.

Example Output

{
  "os": "Windows",
  "timestamp": "2025-04-01T12:00:00Z",
  "tests": [
    {
      "testName": "Net.hello.c_Bit32",
      "sourceFile": "hello.c",
      "targetArch": "Bit32",
      "targetFramework": "Net",
      "nativeCompileTimeMs": 1234,
      "nativeRunTimeMs": 56,
      "cesiumCompileTimeMs": 789,
      "cesiumRunTimeMs": 23,
      "totalTimeMs": 2102
    }
  ],
  "summary": {
    "totalTests": 100,
    "totalNativeCompileTimeMs": 12345,
    "totalCesiumCompileTimeMs": 67890,
    "totalTimeMs": 80235
  }
}

Fixes #985

[ForNeVeR]

Sadly, compilation breaks in this PR, would you please take a look?