Function clip_segment_single

Clip a single segment to the nD slice and return interpolation parameters.

Returns [visible, t1, t2] where:

• visible: 1.0 if any part of segment intersects slice, 0.0 otherwise
• t1: interpolation parameter for clipped start (0.0 = original start)
• t2: interpolation parameter for clipped end (1.0 = original end)

MED-20: pass workspace (length >= ndim) to avoid per-call Uint8Array allocation in hot loops; the buffer is zeroed by this function before use.