Convenience for the common case in _performRequestInternal: derive the
next sleep duration from either Retry-After (server-directed) or the
exponential fallback, always bounded by opts.maxMs.
Returned value is non-negative integer-ms suitable for setTimeout.
Convenience for the common case in
_performRequestInternal: derive the next sleep duration from eitherRetry-After(server-directed) or the exponential fallback, always bounded byopts.maxMs.Returned value is non-negative integer-ms suitable for
setTimeout.