Add XML namespace support for Choice properties

[GregoryNikolaishvili]

• Support XmlTag.Namespace for per-property XML namespaces
• Emit [XmlElement(..., Namespace=...)] for correct XML output
• Serialize only the active choice property (no xsi:nil)
• Add advanced XML serialization tests with namespaces
• Add envelope and document models for test coverage
• Update tests for mixed XmlTag/XmlElement and namespaces
• Bump version to 2.2.0

[Copilot]

Pull request overview

This PR extends the Choice source generator’s XML serialization support by allowing per-property XML namespaces (via XmlTag.Namespace) and by tightening XML output so only the active choice property is serialized (avoiding xsi:nil for inactive choices). It also adds a set of namespace-focused serialization tests and updates the package version.

Changes:

• Add Namespace support to XmlTagAttribute and propagate it into generated [XmlElement(..., Namespace = ...)] attributes.
• Generate ShouldSerialize{Property}() methods for choice properties to ensure only the active choice serializes (no xsi:nil for inactive choices).
• Add/expand XML serialization tests covering namespaces, envelope/document structures, and nil suppression; bump version to 2.2.0.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/AltaSoft.ChoiceGenerator.Tests/XmlNamespaceNilTests.cs	Adds regression tests asserting no xsi:nil and no inactive choice elements are emitted.
tests/AltaSoft.ChoiceGenerator.Tests/XmlNamespaceChoice.cs	Introduces a Choice model using XmlTag.Namespace for per-property namespaces.
tests/AltaSoft.ChoiceGenerator.Tests/XmlChoiceSerializationTests.cs	Adds comprehensive XML round-trip tests for multiple choice shapes and edge cases.
tests/AltaSoft.ChoiceGenerator.Tests/ChoiceGeneratorTests.cs	Adds namespace round-trip tests for XmlNamespaceChoice.
tests/AltaSoft.ChoiceGenerator.Tests/AdvancedXmlNamespaceTests.cs	Adds advanced envelope/document namespace tests and nil suppression checks.
tests/AltaSoft.ChoiceGenerator.Tests/AdvancedXml/*	Adds XML models used for advanced namespace/envelope serialization coverage.
tests/AltaSoft.Choice.Generator.SnapshotTests/Snapshots/*	Updates/introduces snapshots reflecting namespace emission and ShouldSerialize behavior changes.
tests/AltaSoft.Choice.Generator.SnapshotTests/ChoiceGeneratorTest.cs	Adds snapshot test cases for XmlTag.Namespace and mixed attribute scenarios.
src/AltaSoft.Choice/XmlTagAttribute.cs	Adds Namespace property to XmlTagAttribute.
src/AltaSoft.Choice.Generator/Models/PropertyDetails.cs	Stores per-property XML namespace metadata for generation.
src/AltaSoft.Choice.Generator/Executor.cs	Emits [XmlElement(..., Namespace=...)] and generates ShouldSerialize{Property} methods for choices.
Directory.Build.props	Bumps version to 2.2.0 and updates copyright years.

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