fix(normalisation): retry on ValueError when sampling null ensemble

[cbueth]

The @normalise_against_random decorator generates directed $G(n,m)$ random graphs and feeds them to the metric function to build the null distribution. For small graphs, a random graph can coincidentally end up with a perfectly symmetric adjacency matrix (all edges reciprocated). The reciprocity metric rejects such matrices with ValueError, causing a flaky test failure.

Fix: catch ValueError from the metric function during the sampling loop and retry with a fresh random graph. A for...else guard raises RuntimeError if valid samples cannot be collected within n_rand_val x 10 attempts, ensuring the null distribution always has exactly the requested number of samples.

[codspeed-hq]

Merging this PR will degrade performance by 24.76%

⚠️ 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]	1.4 ms	1.8 ms	-24.76%

Tip

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

---

_{Comparing fix/flaky-reciprocity-test (c29af52) with main (33476c0)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (875adcd) to head (c29af52).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #52   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           29        29           
  Lines          842       866   +24     
  Branches       151       150    -1     
=========================================
+ Hits           842       866   +24     

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