Give JWK independent value semantics for thread-safe copies

CHANGELOG.md

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+# Changelog
+
+## 0.5.0 - 2026-09-29
+
+### Added
+
+- Parsed `JWK` and `JwkSet` values now own their key material and metadata
+  allowing copies can be safely passed to worker threads without sharing
+  mutable JSON state.
+- Added `%jwk` serialization, which produces an independent `JsonNode` and
+  retains extension members.
+- The unit-test task now runs under threaded ARC and ORC memory management, with
+  coverage for copied key caches used concurrently by workers.
+
+### Changed
+
+- `initJwk` now snapshots its input JSON. Mutating the source `JsonNode` after
+  parsing no longer changes the resulting key.
+- `jwk["member"]` still returns `Option[JsonNode]`, but the node is now a fresh
+  copy. Mutating it no longer changes the key; construct a new key with
+  `initJwk` to make a modification.