feat: update field constants from labkit-spec v1.0

    # GitLab pipeline numeric ID.

    GL_PIPELINE_ID = "gl_pipeline_id"

    # GitLab namespace numeric ID.

    GL_NAMESPACE_ID = "gl_namespace_id"

    # GitLab root (top-level) namespace numeric ID.

    GL_ROOT_NAMESPACE_ID = "gl_root_namespace_id"

    # Log event timestamp in ISO 8601 format (e.g. "2026-04-02T12:00:00.000Z").

    TIMESTAMP = "timestamp"

    # The endpoint_id of the original caller at the root of the call chain.

    ROOT_CALLER_ID = "root_caller_id"

    # GitLab SentNotification record numeric ID associated with an incoming

    # email reply.

    GL_SENT_NOTIFICATION_ID = "gl_sent_notification_id"

    # Maps each field constant to its logging field variant version.

    # A version of 0 means the field is not yet assigned to any variant.

    VARIANT_VERSION = {

      TTFB_S => 0,

      GL_PROJECT_ID => 1,

      GL_PIPELINE_ID => 1,

      GL_NAMESPACE_ID => 0,

      GL_ROOT_NAMESPACE_ID => 0,

      TIMESTAMP => 0,

      SEVERITY => 0,

      LOG_MESSAGE => 1,

      ENDPOINT_ID => 0,

      CALLER_ID => 1,

      ROOT_CALLER_ID => 0,

      GL_SENT_NOTIFICATION_ID => 0,

    }.freeze

    # Get the constant name for a field value