Fix #11 & #12

[WhiffleFish]

• Add new NativeSARSOP.solve_info that returns the policy as well as an info NamedTuple containing the tree, total planning time, and the total number of planning iterations.
• Remove unnecessary ba_action field from the tree. This is leftover from when raw POMDP inputs were used for planning instead of the SparseTabular form we use now.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (a008194) 99.27% compared to head (cddc962) 99.27%.

❗ Current head cddc962 differs from pull request most recent head 9011393. Consider uploading reports for the commit 9011393 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   99.27%   99.27%           
=======================================
  Files          12       12           
  Lines         690      691    +1     
=======================================
+ Hits          685      686    +1     
  Misses          5        5           

Impacted Files	Coverage Δ
src/tree.jl	100.00% <ø> (ø)
src/solver.jl	100.00% <100.00%> (ø)

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