Boost 1.90 marks deadline_timer deprecated; keep historical type aliases so existing spinscale tests need no renames.
Co-authored-by: Cursor <cursoragent@cursor.com>
Move ProbeComponentThreadHarness into spinscale_probe_support (sscl::probe) so tools can link it without gtest; keep a sscl::tests compatibility shim.
Co-authored-by: Cursor <cursoragent@cursor.com>