fix: execution order of OnlyOnce callbacks

[vbreuss]

This PR fixes the execution order of OnlyOnce callbacks in the Mockolate mocking library. The issue was that callbacks configured with OnlyOnce() were being executed in reverse order due to an incorrect index increment operation.

Key changes

• Removed premature index increment in Callback.Invoke method that was causing callbacks to execute in reverse order
• Added comprehensive test to verify sequential execution of multiple OnlyOnce callbacks

[Copilot]

Pull request overview

This PR fixes the execution order of OnlyOnce callbacks in the Mockolate mocking library. The issue was that callbacks configured with OnlyOnce() were being executed in reverse order due to an incorrect index increment operation.

• Removed premature index increment in Callback.Invoke method that was causing callbacks to execute in reverse order
• Added comprehensive test to verify sequential execution of multiple OnlyOnce callbacks

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Source/Mockolate/Setup/Callback.cs	Removed Interlocked.Increment(ref index) call that was causing callbacks to execute in reverse order
Tests/Mockolate.Tests/MockMethods/SetupMethodTests.cs	Added test MultipleOnlyOnceCallbacks_ShouldExecuteInOrder to verify correct sequential execution of multiple OnlyOnce callbacks

[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   5m 14s ⏱️ - 1m 3s
 1 792 tests +1   1 791 ✅ +1  1 💤 ±0  0 ❌ ±0 
11 973 runs  +7  11 972 ✅ +7  1 💤 ±0  0 ❌ ±0 

Results for commit 3956073. ± Comparison against base commit 5069c06.

[github-actions]

🚀 Benchmark Results

Details

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

AMD EPYC 7763 2.45GHz, 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	1.433 μs	0.0072 μs	0.0064 μs	0.2232	-	3.66 KB
Simple_Moq	181.568 μs	0.5532 μs	0.4620 μs	0.4883	-	14.55 KB
Simple_NSubstitute	5.733 μs	0.0193 μs	0.0161 μs	0.5569	0.0076	9.14 KB
Simple_FakeItEasy	6.193 μs	0.0101 μs	0.0084 μs	0.4959	-	8.11 KB

[github-actions]

This is addressed in release v0.47.0.