fix: use _sample_inspirations in sample_from_island for consistent inspiration selection

[octo-patch]

Fixes #437

Problem

sample_from_island() selects inspiration programs using plain random.sample() from island program IDs, while sample() delegates to the much richer _sample_inspirations() method. This inconsistency means that the parallel execution path (process_parallel.py → sample_from_island) misses:

• Prioritising the island's best program as an inspiration
• Including top-ranked programs from the island (elite selection ratio)
• Selecting programs from nearby MAP-Elites feature cells for diversity

Solution

Replace the ad-hoc random sampling block in sample_from_island() with a call to _sample_inspirations(parent, n=num_inspirations). Because _sample_inspirations derives the target island from parent.metadata["island"] — and the parent was sampled from the correct island — the method automatically scopes sampling to the right island, maintaining the same island isolation guarantee.

Testing

• All 370 existing unit tests pass (python -m unittest discover tests)
• The change is a pure behavioural alignment: no interface changes, no new parameters

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