docs: add Vlasov 1D docstring coverage

[joglekara]

Summary

• Add module, class, constructor, callable, and helper docstrings across the Vlasov 1D implementation package
• Cover Pydantic config models, simulation/domain objects, storage callbacks, vector-field composition, and numerical pushers
• Add a docstring to the public adept.vlasov1d entry point

Verification

• uvx ruff format adept/_vlasov1d adept/vlasov1d.py
• uvx ruff check adept/_vlasov1d adept/vlasov1d.py
• AST docstring coverage scan over adept/_vlasov1d and adept/vlasov1d.py
• uv run pytest tests/test_vlasov1d -q → 80 passed, 7 deselected, 1 xpassed