Add typed update policy support

[HituziANDO]

Problem

The framework can show a default update alert but cannot model common product policies such as optional updates, required minimum versions, skipped versions, or a reminder interval. Applications must rebuild this logic around loosely coupled callbacks.

Scope

• Define typed optional and required update policies.
• Support a caller-provided minimum supported version.
• Support skipping a specific version and configuring the next reminder interval.
• Keep policy evaluation independent of any remote-config vendor.
• Allow custom and built-in presenters to consume the same policy result.

Dependencies

• Replace fixed-width version encoding with validated three-way ordering #19
• Extract UpdateCheckService and add a structured async API #23

Acceptance criteria

• Optional, required, skipped, and deferred outcomes are explicit values.
• Required updates cannot accidentally expose a remind-later action.
• Policy evaluation is deterministic and independently testable.
• Current behavior remains the default when no policy is supplied.

Tests

• Cover version boundaries, skip persistence, reminder expiry, required-update presentation, and policy changes.

Relevant files

• Framework/Sources/SUK.swift
• Framework/Sources/SwiftyUpdateKitConfig.swift