Add Roslyn analyzers for string optimization patterns

- Implemented 8 diagnostic rules (OPENTXT001-008) for detecting inefficient string patterns
- Created analyzers for: Substring, Split, string concatenation, IndexOf+Substring, Trim+Equals
- Added code fix provider for Split patterns
- Comprehensive test suite with smart detection tests to prevent false positives
- Extensive documentation: README, EXAMPLES, CONTRIBUTING, TESTING_STRATEGY, QUICK_REFERENCE
- Integrated into solution with proper NuGet package configuration
- Analyzers use semantic analysis for type safety and context-aware suggestions

Author: electricessence

Analyzers.Tests/Open.Text.Analyzers.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Analyzer.Testing.XUnit" Version="1.1.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.XUnit" Version="1.1.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="xunit" Version="2.6.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="6.0.0">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Analyzers\Open.Text.Analyzers.csproj" />
+  </ItemGroup>
+
+</Project>