Tighten exactness with MATLAB fixtures and release gate

[iahncajigas]

Summary

• replace the approximate place-cell basis with MATLAB-normalized Zernike functions and regenerate the affected parity notebooks
• add MATLAB gold-fixture export plus Python-side fixture tests for SignalObj, nspikeTrain, CIF, and point-process simulation prefixes
• add a standard release-gate command that runs fixture refresh, parity tests, notebook checks, and the MATLAB python_port_fidelity suite

Verification

• pytest -q tests/test_zernike.py tests/test_matlab_gold_fixtures.py tests/test_release_check.py tests/test_notebook_fidelity_audit.py tests/test_notebook_parity_notes.py tests/test_parity_report.py tests/test_signalobj_fidelity.py tests/test_nspiketrain_fidelity.py tests/test_workflow_fidelity.py
• python tools/notebooks/run_notebooks.py --group helpfile_full --topics HippocampalPlaceCellExample --timeout 1200
• matlab -batch "cd('/Users/iahncajigas/Library/CloudStorage/Dropbox/Codex/nSTAT'); addpath(pwd); addpath(fullfile(pwd,'helpfiles')); results = runtests('tests/python_port_fidelity'); assertSuccess(results); exit"