PML-385: generator seed for Latent space of theQGAN

[CassNot]

Summary

Adds support for passing a dedicated torch.Generator to PhotonicGenerator.sample_latent() and PhotonicGenerator.generate()
This enables reproducible latent batches without advancing PyTorch’s global random-number generator
Backward compatibility is ensured.

Related Issue

PML-385

Type of change

• Bug fix
• New feature
• Documentation update
• Refactor / Cleanup
• Performance improvement
• CI / Build / Tooling
• Breaking change (requires migration notes)

Proposed changes

Added the generator parameter to:

• LatentDistribution.sample()
• NormalLatent.sample()
• PhotonicGenerator.sample_latent()
• PhotonicGenerator.generate()

Preserved compatibility with custom latent distributions implemented before the new parameter existed.
Added tests covering:

• Reproducibility with an explicit generator.
• Preservation of global RNG state.
• Generator support through generate().
• Backward compatibility with legacy latent distributions.

Updated the QGAN documentation and photonic QGAN reproduction notes.

How to test / How to run

1. Command lines

pytest tests/models/test_photonic_generator.py

Documentation

• User docs updated (Sphinx)
• Examples / notebooks updated
• Docstrings updated
• Updated the API

Checklist

• PR title includes Jira issue key (e.g., PML-126)
• "Related Jira ticket" section includes the Jira issue key (no URL)
• Code formatted (ruff format)
• Lint passes (ruff)
• Static typing passes (mypy) if applicable
• Unit tests added/updated (pytest)
• Tests pass locally (pytest)
• Tests pass on GPU (pytest)
• Test coverage not decreased significantly
• Docs build locally if affected (sphinx)
• With this command: SPHINXOPTS="-W --keep-going -n" make -C docs clean html the docs are built without any warning or errors.
• New public classes/methods/packages are added in the API following the methodology presented in other files.
• Dependencies updated (if needed) and pinned appropriately
• PR description explains what changed and how to validate it