Add some optional serde implementations, as well as .clone on BVH

[aidanhs]

No description provided.

[svenstaro]

I'm generally fine with this but make the CI happy. :)

[aidanhs]

Looks like nightly just flat-out breaks a dependency deep in the tree (num-bigint)

rust-num/num-bigint#219
rust-lang/rust#88617

I'll wait until num-bigint gets a patch and then prompt CI to rerun.

[aidanhs]

First-time contributors need a maintainer to approve running workflows.

Can you approve? 😄

[codecov-commenter]

Codecov Report

Merging #74 (46cc3f1) into master (4554a9a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #74   +/-   ##
=======================================
  Coverage   80.11%   80.11%           
=======================================
  Files           9        9           
  Lines        1564     1564           
=======================================
  Hits         1253     1253           
  Misses        311      311           

Impacted Files	Coverage Δ
src/aabb.rs	93.29% <ø> (ø)
src/bvh/bvh_impl.rs	61.72% <ø> (ø)

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[svenstaro]

Cool, thanks!

[aidanhs]

Thanks for quick merge!