docs: remove mutation testing badge

[vbreuss]

This PR removes the mutation testing badge from the README due to current incompatibility with the Testing Platform.

• Removes the Stryker mutation testing badge from the repository documentation

[Copilot]

Pull request overview

This PR removes the mutation testing badge from the README due to current incompatibility with the Testing Platform.

• Removes the Stryker mutation testing badge from the repository documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

    14 files  ±0      14 suites  ±0   4m 33s ⏱️ +10s
 1 534 tests ±0   1 533 ✅ ±0  1 💤 ±0  0 ❌ ±0 
10 227 runs  ±0  10 226 ✅ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit e6b007f. ± Comparison against base commit 436f685.

[github-actions]

🚀 Benchmark Results

Details

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.3 LTS (Noble Numbat)

AMD EPYC 7763 2.64GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.101

[Host] : .NET 10.0.1 (10.0.1, 10.0.125.57005), X64 RyuJIT x86-64-v3
Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Simple_Mockolate	1.513 μs	0.0297 μs	0.0278 μs	0.2232	-	3.66 KB
Simple_Moq	180.183 μs	4.7896 μs	4.2459 μs	0.4883	-	14.55 KB
Simple_NSubstitute	5.988 μs	0.0917 μs	0.0858 μs	0.5493	0.0076	9.09 KB
Simple_FakeItEasy	6.446 μs	0.1420 μs	0.1328 μs	0.4959	-	8.11 KB

[github-actions]

This is addressed in release v0.44.0.