release: 4.16.1 (#679)

* codegen metadata

* docs: add comment for arbitrary value fields

* chore(internal): correct cache invalidation for `SKIP_MOCK_TESTS`

* fix(client): preserve time zone in lenient date-time parsing

* release: 4.16.1

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Co-authored-by: stainless-app[bot] <142633134+stainless-app[bot]@users.noreply.github.com>