SLG-0004: Metadata privacy levels implementation

[kukushechkin]

This implements the SLG-0004 proposal introducing an attributed metadata system that allows attaching attributes to metadata values. Privacy level is the first concrete attribute, enabling developers to mark metadata values as .private or .public so LogHandler implementations can redact sensitive values before logging.

Motivation:

SwiftLog lacks a mechanism to attach attributes to metadata values as sensitive to allow Log Handlers to control logging behavior.

Modifications:

• Attributed metadata added.
• Privacy levels can be attached to Attributed Metadata via string interpolation.
• Logger and LogHandler have new API surface for using Attributed Metadata.

Result:

Sensitive metadata values can be marked as .private to signal compatible Log Handlers to mask the value when logging.