Latest modifier

[ra1028]

Pull Request Type

• Bug fix
• New feature
• Refactoring
• Documentation update
• Chore

[Copilot]

Pull Request Overview

Adds a new LatestModifier and Atom.latest(_:) API to retain and expose the most recent value whose Boolean key path evaluates to true, along with tests and documentation updates.

• Introduces LatestModifier and Atom.latest(_:) convenience.
• Adds comprehensive test coverage for validity retention behavior.
• Updates docs (Docs + README) to list and demonstrate the new modifier.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Tests/AtomsTests/Modifier/LatestModifierTests.swift	Adds unit tests covering core behaviors and key identity of LatestModifier.
Sources/Atoms/Modifier/LatestModifier.swift	Implements the LatestModifier and Atom.latest(_:) API including storage mechanism.
Sources/Atoms/Atoms.docc/Atoms.md	Documents the new modifier in the modifiers index.
README.md	Adds README section with usage example for latest(_:)

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