Define cached threshold behavior for isEnabled

Document and test explicit refresh boundaries for isEnabled guards, and
only read the shared root threshold when no namespace threshold applies.
Include the portable Nimble configuration loader.

tests/README.md

@@ -84,7 +84,11 @@ the unsafe forms are tested as compilation failures.
 
 The in-process regression tests are deterministic. The lifetime suite checks
 copying, self-assignment, replacement, moving, container copies, and exporting a
-handle from a local service. Refresh tests verify that repeated clone failures
+handle from a local service. `isEnabled` tests verify that namespace thresholds
+remain cached until an explicit refresh, a logging call, or `getLogger`, while
+the root fallback is read from shared state. This behavior is intentional so
+guards can avoid configuration refresh work.
+Refresh tests verify that repeated clone failures
 preserve the old appenders and thresholds, release partial replacements, and
 allow a later retry without another configuration change. A successful refresh
 releases the replaced cache and installs both appenders and thresholds.
@@ -113,8 +117,8 @@ The suite provides targeted regressions; it does not exhaust thread scheduling
 or ORC cycle-collector interleavings.
 
 The ownership scenarios, lifetime suite, and appender-state cleanup regression
-exercise the new ownership contracts. `isEnabled` freshness,
-local-time timestamp construction, and allocator reports remain for
+exercise the new ownership contracts. Local-time timestamp construction and
+allocator reports remain for
 subsequent work.
 
 The standalone `ownership.nim` regression suite passed AddressSanitizer and