MSC3999: Add causal parameter to `/timestamp_to_event`#3999

MadLittleMods wants to merge 4 commits intomainmatrix-org/matrix-spec-proposals:mainfrom

madlittlemods/timestamp-to-event-causality-parametermatrix-org/matrix-spec-proposals:madlittlemods/timestamp-to-event-causality-parameterCopy head branch name to clipboard