Function reconstruct_node 

pub fn reconstruct_node(
    approximation: &[f64],
    detail: &[f64],
    wavelet: &dyn Wavelet,
    boundary_mode: BoundaryMode,
) -> Result<Vec<f64>>

Reconstruct a parent node from its two children using an inferred length.

This preserves the pre-2.0 public helper at ferro_wave::transform::wpt::reconstruct_node. It can infer a unique parent length for biorthogonal lifting (approximation.len() + detail.len()). For orthogonal wavelets the DWT band length has a parity ambiguity, so this wrapper chooses the larger valid parent length for the (band_len, filter_len, boundary) triple. For exact WPT reconstruction, prefer iwpt or call reconstruct_node_with_length with the recorded parent length.