fn resolve_flush_reason(
explicit_reason: Option<FlushReason>,
request_reason: Option<RegionFlushReason>,
is_downgrading: bool,
) -> FlushReasonfn resolve_flush_reason(
explicit_reason: Option<FlushReason>,
request_reason: Option<RegionFlushReason>,
is_downgrading: bool,
) -> FlushReason