Feat/pox getters

[jcnelson]

This addresses #2538 by adding getters in .pox-2 for state that is currently invisible. It also adds basic unit tests to verify that the getters work as you'd expect.

[codecov]

Codecov Report

Merging #3166 (9f10bfb) into next (6376520) will increase coverage by 0.41%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             next    #3166      +/-   ##
==========================================
+ Coverage   83.93%   84.34%   +0.41%     
==========================================
  Files         272      272              
  Lines      213424   213695     +271     
==========================================
+ Hits       179129   180248    +1119     
+ Misses      34295    33447     -848     

Impacted Files	Coverage Δ
src/chainstate/stacks/boot/pox_2_tests.rs	93.90% <100.00%> (+1.51%)	⬆️
src/burnchains/bitcoin/network.rs	81.01% <0.00%> (-0.47%)	⬇️
src/util_lib/bloom.rs	92.59% <0.00%> (-0.42%)	⬇️
src/burnchains/bitcoin/spv.rs	76.70% <0.00%> (-0.33%)	⬇️
src/net/poll.rs	62.43% <0.00%> (-0.26%)	⬇️
src/chainstate/coordinator/mod.rs	90.59% <0.00%> (-0.16%)	⬇️
src/net/http.rs	76.90% <0.00%> (-0.09%)	⬇️
src/net/connection.rs	84.03% <0.00%> (-0.07%)	⬇️
src/chainstate/stacks/transaction.rs	96.32% <0.00%> (-0.05%)	⬇️
src/chainstate/stacks/index/storage.rs	81.62% <0.00%> (ø)
... and 29 more

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[pavitthrap]

For the work in #3035, could you make current-pox-reward-cycle and burn-height-to-reward-cycle non private?

[kantai]

This looks good to me, but I agree with @pavitthrap's request for making two currently private methods read-only.

[jcnelson]

Done 👍

[kantai]

LGTM!