Support negation and decimal literals in OData filter queries (#28)

Adds handling for "not <field> <op> <value>" expressions, which OData
parses as "(not <field>) <op> <value>", by wrapping the underlying
comparison in a MUST_NOT boolean clause. Also adds decimal literal
support and switches float range queries to double ranges to match
how numeric fields are indexed. Introduces an xUnit test project
covering the visitor and LuceneNetIndexSearcher.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: paulirwin

AzureSearchEmulator.UnitTests/AzureSearchEmulator.UnitTests.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+	<PropertyGroup>
+		<TargetFramework>net10.0</TargetFramework>
+		<Nullable>enable</Nullable>
+		<ImplicitUsings>enable</ImplicitUsings>
+		<IsTestProject>true</IsTestProject>
+		<WarningsAsErrors>nullable</WarningsAsErrors>
+		<IsPackable>false</IsPackable>
+	</PropertyGroup>
+
+	<ItemGroup>
+		<PackageReference Include="xunit" Version="2.9.3" />
+		<PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
+			<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+			<PrivateAssets>all</PrivateAssets>
+		</PackageReference>
+		<PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<ProjectReference Include="..\AzureSearchEmulator\AzureSearchEmulator.csproj" />
+	</ItemGroup>
+
+</Project>