feat(pl): Type conversions

[contagon]

There was a LOT of redundant converting between types code happening all over the codebase (oh how I miss Rust's .into()!), so all of it was moved into a new templated convert function. This should help with writing new pipelines, and makes convert containers types a lot easier.

Still todo:

• Make sure results are still the same
• Make vector conversion work with custom allocates (ct-icp in particular needs this)
• Verify new convert functions make it into the python wheel

[contagon]

Verified results are all the same. The exception is lio-sam which I'm not getting consistent results out of which isn't terribly surprising.