Cache TerminationStatus to fix performance

[odow]

Closes #204

[codecov]

Codecov Report

Base: 58.93% // Head: 58.97% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (b1fdec9) compared to base (da62d14).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #205      +/-   ##
==========================================
+ Coverage   58.93%   58.97%   +0.04%     
==========================================
  Files           3        3              
  Lines         526      529       +3     
==========================================
+ Hits          310      312       +2     
- Misses        216      217       +1     

Impacted Files	Coverage Δ
src/MOI_wrapper/MOI_wrapper.jl	86.94% <100.00%> (-0.22%)	⬇️

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[odow]

(cbc) pkg> st
      Status `/private/tmp/cbc/Project.toml`
  [9961bab8] Cbc v1.0.1 `~/.julia/dev/Cbc`
  [4076af6c] JuMP v1.3.0

julia> using JuMP

julia> import Cbc

julia> function main(M)
           model = Model(Cbc.Optimizer)
           set_silent(model)
           @variable(model, x[1:2M], Int)
           @variable(model, y[1:7_800M])
           optimize!(model)
           @time sol = value.(all_variables(model))
           return sol
       end
main (generic function with 1 method)

julia> @time main(10);
  0.036092 seconds (858.24 k allocations: 19.263 MiB)
  0.162443 seconds (1.58 M allocations: 76.591 MiB, 10.14% compilation time)

julia> @time main(100);
  0.449334 seconds (8.58 M allocations: 181.622 MiB, 15.22% gc time)
  2.001931 seconds (15.61 M allocations: 642.915 MiB, 15.17% gc time)