[BUG] Fix HidalgoSegmenter IndexError with empty sampling (Fixes #3168)

[samay2504]

Fixes #3168
Fixes #3150

Problem

HidalgoSegmenter crashes with IndexError: too many indices for array when configured with incompatible burn_in and sampling_rate parameters that result in zero samples passing the filtering criteria.

Root Cause

The _fit() method filters samples using:

idx = [it for it in range(n_iter) if it % sampling_rate == 0 and it >= n_iter * burn_in]

Solution:

1. Initialize bestsampling = None to detect empty filtering
2. Skip replicas with empty idx to allow later replicas a chance to produce samples
3. Validate non-empty result with informative error message
4. Fix Pi normalization to use actual sample count instead of hardcoded K

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[Copilot]

Pull request overview

This PR fixes a critical IndexError bug in HidalgoSegmenter that occurs when incompatible burn_in and sampling_rate parameters result in zero valid samples after filtering. The fix adds proper validation and error handling to detect and report this configuration issue with a helpful error message.

Key changes:

• Added empty sample detection with early continue for individual replicas
• Implemented validation to ensure at least one replica produces valid samples
• Corrected Pi normalization to use actual sample count instead of the number of manifolds (K)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
test_hidalgo_fix.py	New test file with three test cases covering empty sampling error, valid configuration, and boundary cases
aeon/segmentation/_hidalgo.py	Bug fix implementation including empty sample handling, validation error, and Pi normalization correction

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[MatthewMiddlehurst]

Sorry for only getting around to this now. We had 3 PRs on this and 2 issues I believe, but going with this. Made some changes to speed up and get this tidied quicker, including moving the tests.

[TonyBagnall]

thank you for this @samay2504 sorry it took so long to get in!