fix: handle rejected final samples in test mode 1

[Jammy2211]

Summary

Prevent PYAUTO_TEST_MODE=1 from finalizing a sampler point whose model reconstruction raises FitException. Reduced searches now replace that rejected point with bounded, deterministic, fully validated representative samples, preserving valid result creation and downstream chaining while failing clearly when no valid representative exists.

Fixes #1462.

API Changes

NonLinearSearch.fit() changes behavior only under PYAUTO_TEST_MODE=1: a final sample rejected with FitException is replaced by valid representative test-mode samples. Normal searches, test modes 2/3, and non-FitException failures are unchanged.
See full details below.

Test Plan

• Focused rejected-final-sample regression tests: 4 passed
• Surrounding search tests: 32 passed
• Full PyAutoFit suite: 1707 passed, 2 skipped
• git diff --check

Full API Changes (for automation & release notes)

Changed Behaviour

• autofit.non_linear.search.abstract_search.NonLinearSearch.fit() — under PYAUTO_TEST_MODE=1, validates the final summary instance and replaces a FitException-rejected result with bounded deterministic representative samples.
• Replacement samples are all validated before result creation; failure after 100 attempts raises a clear FitException.
• Production behavior and unrelated exception propagation are unchanged.

Migration

• None required.

Generated by the PyAutoLabs agent workflow.