fix diff engine converter bugs: 1D matmul dims, reshape, transpose, q…

[Transurgeon]

…uad form

• helpers.py: fix 1D dimension normalization in dense matmul helpers. Right-matmul treated 1D A as (1,n) instead of (n,1), causing segfaults.
• converters.py: reshape 1D child to column vector in left-matmul for dot products; add constant-atom fallback for unfolded expressions; move QuadForm/SymbolicQuadForm dispatch out of ATOM_CONVERTERS (needs n_vars); tolerate 1D dimension mismatches via reshape instead of error.
• registry.py: support C-order reshape via transpose decomposition; fix 1D transpose to be a no-op; improve scalar quad form P handling; raise NotImplementedError for vector SymbolicQuadForm (TODO: native block quadform in SparseDiffPy).
• perspective_canon.py: handle DiffengineConeProgram which stores q, d, A, b as separate arrays (vs ParamConeProg sparse tensors).

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• New feature (backwards compatible)
• New feature (breaking API changes)
• Bug fix
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