[Configuration] WritableOptions depends on IOptionsMonitor<T> although only IOptionsSnapshot<T> functionality is used

[DevTKSS]

What would you like to be changed

Replace the dependency on IOptionsMonitor<T> with IOptionsSnapshot<T>:

• Change the constructor dependency and internal field type in WritableOptions<T>
• Update WritableOptions.Value to use _options.Value instead of _options.CurrentValue
• Adjust the service registration in ConfigureAsWritable<T> accordingly
  (currently the only registration site; VS Code navigation already points to this class)

Why is this needed

WritableOptions<T> currently depends on IOptionsMonitor<T>, although it does not provide any monitor-specific functionality such as OnChange event and neither uses them internally.

The implementation only uses functionality that is already provided by IOptionsSnapshot<T>:

• .Get(name)
• CurrentValue which is equivalent to IOptionsSnapshot<T>.Value

This is also reflected in the public API:

• IWritableOptions<T> inherits from IOptionsSnapshot<T>, not IOptionsMonitor<T>

Reducing the dependency to IOptionsSnapshot<T> would:

• better align implementation with the exposed interface
• avoid unnecessary higher-privilege options access
• simplify the mental model for consumers

For which platform

• All platforms

Anything else we need to know?