Get Mcp Sql Stages

Where the time of a run_sql (or, with tool=get_series, a get_series) call goes: p50 and p95 per stage over the last days days, next to the same percentiles for the whole call.

Stages are the keys of mcp_tool_calls.timings (auth, parse, cache, db_connect, db_execute, enrich, serialise, log; see routers/agent/call_stats.py). A stage that did not run in a call (no enrichment, say) is absent from that row and so does not pull its percentiles down. unaccounted is the gap between the whole call and the stages on the critical path (everything but log, which is written after the client has its answer).