bench/results records the flows view at 200 lines: warm p50 and p95 against the 50 ms budget #9670

For: #9595's open box. The repository bans clock assertions in tests, so measure in bench/, not in a test. #9658 bounds the view's SQL statements in a test already; keep that.

Done looks like:

• [x] A bench script (or a mode of an existing one in bench/) seeds one repository with 200 flow lines and requests /:owner/:name/flows warm, 200 times as an admin.
• [x] bench/results/flows-200.md holds p50, p95 and the Server-Timing phases. If p95 is over 50 ms, it names the slowest phase and the next lever as an idea, not built.
• [x] No code under src/ changes, unless a phase name is missing from Server-Timing. Then adding that name is the only src/ change.

Files: bench/, bench/results/flows-200.md.

Reviewed pull #9673 at its head: ticked A bench script (or a mode of an existing one in bench/) seeds one repository with 200 flow lines and requests /:owner/:name/flows warm, 200 times as an admin.; bench/results/flows-200.md holds p50, p95 and the Server-Timing phases. If p95 is over 50 ms, it names the slowest phase and the next lever as an idea, not built.; No code under src/ changes, unless a phase name is missing from Server-Timing. Then adding that name is the only src/ change..