Add Gauge support

[Kyle-Ye]

Summary

Add public Gauge support for displaying a value within a bounded range.

Scope

• Add the public Gauge API and its common value-in-range initializers.
• Support labels for the gauge, current value, minimum value, maximum value, and marked values where applicable.
• Integrate GaugeStyle, style configuration, .gaugeStyle(_:), and baseline platform-appropriate presentations.
• Normalize and update gauge values while preserving the supplied range and label content.
• Add examples and focused coverage for simple and fully labeled gauges.

Acceptance criteria

• A basic Gauge(value:in:label:) compiles and renders on supported hosts.
• Current, minimum, and maximum value labels are available to gauge styles.
• Applying a supported gauge style changes the presentation without changing the underlying value semantics.
• Updating the value or range updates the rendered gauge while preserving view identity.

API reference

• Gauge