Refactor the state of search expressions as OneOrMany.

[fiseni]

It addresses the issue #506

[Copilot]

Pull Request Overview

This PR replaces the internal List<SearchExpressionInfo<T>>? with the new OneOrMany<SearchExpressionInfo<T>> abstraction across the specification, evaluator, and validator layers, and adds tests to cover single and null-property search cases.

• Introduced OneOrMany<SearchExpressionInfo<T>> in Specification<T> and wired it through validators and evaluators.
• Updated sorted insertion logic in OneOrMany<T>.AddSorted and added SearchExpressionComparer<T>.
• Added unit tests for single-search scenarios, including handling of null properties.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/.../SearchValidatorTests.cs	New test for null-property search in SearchValidator
tests/.../SearchMemoryEvaluatorTests.cs	New test for single-search filtering in SearchMemoryEvaluator
src/Ardalis.Specification/Validators/SearchValidator.cs	Switched to OneOrManySearchExpressions and added single-case branch
src/Ardalis.Specification/Specification.cs	Replaced nullable List<SearchExpressionInfo<T>> with OneOrMany<SearchExpressionInfo<T>>
src/Ardalis.Specification/Internals/OneOrMany.cs	Tweaked comparison in AddSorted (changed <= to <)
src/Ardalis.Specification/Expressions/SearchExpressionInfo.cs	Added SearchExpressionComparer<T> for sorted insertion
src/Ardalis.Specification/Evaluators/SearchMemoryEvaluator.cs	Added SpecSingleLikeIterator and used OneOrManySearchExpressions
src/Ardalis.Specification.EntityFrameworkCore/Evaluators/SearchEvaluator.cs	Updated to use OneOrManySearchExpressions in EF evaluator

Comments suppressed due to low confidence (1)

tests/Ardalis.Specification.Tests/Validators/SearchValidatorTests.cs:66

• [nitpick] The test method name contains a double underscore before 'WithNullProperty'. Consider using a single underscore for consistency and readability.

public void ReturnsFalse_GivenSpecWithSingleSearch__WithNullProperty()