ClickHouse runner: pass data_start_time to aligned query groups #873

Blocked by #868: experiment_run_clickhouse.py only bulk-loads a data file, so there is no live feed whose start to align to.

Problem

With align_to_interval, the query client should evaluate at multiples of T counted from where the data starts, so every arm (ASAPQuery, ClickHouse, ClickHouse + MV) answers over the same samples.

• experiment_run_e2e.py with the paced feeder does this (feat(asap-tools): run sketch-bench workload tables end to end with the paced feeder #841). It waits for an aligned feeder start and writes client_options.data_start_time into each mode's client config.
• experiment_run_clickhouse.py doesn't. feat(asap-tools): render sketch-bench e2e queries as ClickHouse SQL #844's generator (datasets/fake_metric/sketch_bench_workloads.py) sets align_to_interval but no data_start_time. Its eval times can only come from rounding the wall clock down to a multiple of T.

Example (T = 60 s): two arms run at different times, with feeds starting at 10:02:23 and 14:02:42. Rounding the wall clock gives windows that cover different samples in each arm (shifted by 19 s here), so accuracy comparisons mix input differences with sketch error.

The SQL rounds NOW() to a multiple of T, so windows are grid-aligned, but that doesn't give the arms a shared data origin.

Proposed fix

Once the ClickHouse runner feeds data live (#868), have it do what #841 does for experiment_run_e2e.py:

1. Start the feed at the next multiple of the LCM of the aligned intervals (aligned_interval_lcm / aligned_start_ms in experiment_utils/services/paced_feeder.py).
2. Write data_start_time (seconds) into each aligned query group's client_options before the client starts (set_data_start).

The client then evaluates repetition k at data_start_time + (max(1, ceil(starting_delay / T)) + k) * T, the same as for the PromQL runner.

Done when

• ClickHouse-runner configs with align_to_interval carry data_start_time, and every arm's repetition k covers the same samples.
• The wall-clock fallback for align_to_interval without data_start_time is removed from the client, and data_start_time becomes required.

Related: #841, #844, #862.