Implement synchronous gauge APIs for Double and Long types

[batuhansk]

This PR introduces support for synchronous gauges in the OpenTelemetry Swift SDK, complementing the existing observable gauge functionality.

Key Changes:

1. New Protocols:

   • Added DoubleGauge and LongGauge protocols to define synchronous gauge behavior.
   • Extended DoubleGaugeBuilder and LongGaugeBuilder with build() methods for synchronous gauges.

2. SDK Implementation:

   • Implemented DoubleGaugeSdk and LongGaugeSdk classes to handle synchronous gauge recording.
   • Updated DoubleGaugeBuilderSdk and LongGaugeBuilderSdk to support building synchronous gauges.

3. No-op Implementations:

   • Added NoopDoubleGauge and NoopLongGauge for default no-op behavior.

4. Testing:

   • Added unit tests to verify synchronous gauge functionality in BuilderTests and StableMeterProviderTests.
   • Updated example usage in main.swift to demonstrate both observable and synchronous gauges.

Example Usage:

// Synchronous gauge
var gauge = meter.gaugeBuilder(name: "my_gauge").build()
gauge.record(value: 1.0, attributes: ["test": AttributeValue.bool(true)])

// Observable gauge
var observableGauge = meter.gaugeBuilder(name: "my_observable_gauge").buildWithCallback { measurement in
    measurement.record(value: 1.0)
}