v4.3.0

Adds chopper transmission probability approximation for use by non-ray-tracing consumers, e.g., chopcal

What's Changed

• Transmission tests by @g5t in #23
• Follow niess moderator by @g5t in #24
• Weight the transmitted region by how likely a neutron is to get through by @g5t in #25

Full Changelog: v4.2.3...v4.3.0