[kseetharam]

Summary

Adds an in-place setter for the Hamiltonian coefficients of a compiled Lindbladian, so a time-dependent Hamiltonian can be stepped as a sequence of constant-generator steps without recompiling the spec per step:

• LindbladSpec::set_h_coeffs(&[f64]) / h_coeffs() in ppvm-lindblad (the coefficients are only read by compute_action_terms, so the setter is a plain O(num_h_terms) overwrite; jump and Kossakowski data, including the PSD check, are untouched).
• pyo3 binding _LindbladSpec.set_h_coeffs(coeffs) / h_coeffs (ValueError on wrong length, non-1-D, non-float64), and Lindbladian.set_h_coeffs(coeffs) / Lindbladian.h_coeffs in the Python wrapper (accepts any array-like, converts to contiguous float64).
• ppvm.version from package metadata (there was no version attribute).
• The pyproject version carries a local label 0.1.0+hcoeffs; drop it if you prefer.

Use case: Pauli propagation of NMR pulse sequences with shaped pulses and field ramps (piecewise-constant envelopes), where the Hamiltonian strings are fixed and only their coefficients change per sample. For a 54-term Hamiltonian a setter call is 0.25 µs; a recompile of a large Kossakowski-form Lindbladian is minutes.

Test plan

• ppvm-python/test/lindblad/test_h_coeffs.py (9 tests): for random 3- and 5-qubit Lindbladians with Hermitian, σ± and multi-term complex jumps plus a Kossakowski block, after set_h_coeffs(c) the outputs of action_arr, leakage_arr (with and without protected words), generator_arr and six pc_step_arr steps in two truncation modes are np.array_equal to a freshly built Lindbladian with coefficients c; restoring the original coefficients restores the outputs; the getter round-trips and returns a copy; wrong shapes raise and leave the coefficients unchanged.
• The existing test/lindblad folder: 32 passed, 1 skipped.
• cargo check clean (clippy/rustfmt were not available in the toolchain used).

Based on kossakowski-dissipator at 2f4e7f5.

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