Merge progressToken into a request's params._meta.progressToken, per
basic/utilities/progress ("a party ... includes a progressToken in the
request metadata", at params._meta.progressToken). Returns params
unchanged when the token is unset. Any existing _meta keys are preserved.
Exposed so callers can attach a progress token to a hand-built params object
(e.g. for request methods without a dedicated progress-token overload).
Merge progressToken into a request's params._meta.progressToken, per basic/utilities/progress ("a party ... includes a progressToken in the request metadata", at params._meta.progressToken). Returns params unchanged when the token is unset. Any existing _meta keys are preserved. Exposed so callers can attach a progress token to a hand-built params object (e.g. for request methods without a dedicated progress-token overload).