perf(progress): throttle print_progress to 1 Hz instead of every pair

[cbueth]

Previously print_progress was called after every single pair, flushing stdout each time. For a 100-node network that's 9,900 flushes. significant stdbuf overhead.

Replace with rate-limited output: print at most once per second, with a final forced print on the last pair. Applies to both sequential and parallel paths.

Mechanism: track last_print timestamp; only call print_progress when at least 1 second has elapsed (or it's the final pair). Uses Manager.Value in the parallel path for cross-process sharing.

[codspeed-hq]

Merging this PR will degrade performance by 28.1%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 27 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	test_detrend_method[z_score-p10]	1.2 ms	1.7 ms	-28.1%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing perf/throttle-progress (9e22ecd) with main (8119494)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8119494) to head (9e22ecd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #50   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           29        29           
  Lines          851       859    +8     
  Branches       147       149    +2     
=========================================
+ Hits           851       859    +8     

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