Add enumeration staking nft

[vtleonardo]

Scope

ThIs PR adds:

• Adds enumeration to the StakingNFT contracts so the FE can query the user's token IDs.
• Cleans up the Staking contract to reduce duplication of code.

[codecov]

Codecov Report

Merging #183 (67c9d4c) into main (324a82e) will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #183      +/-   ##
==========================================
+ Coverage   48.50%   48.58%   +0.07%     
==========================================
  Files         281      281              
  Lines       40901    40900       -1     
==========================================
+ Hits        19841    19871      +30     
+ Misses      18758    18736      -22     
+ Partials     2302     2293       -9     

Impacted Files	Coverage Δ
consensus/lstate/statechnglocal.go	72.55% <0.00%> (+0.46%)	⬆️
consensus/objs/rs.go	60.65% <0.00%> (+0.78%)	⬆️
peering/active.go	83.96% <0.00%> (+0.94%)	⬆️
consensus/lstate/engine.go	53.21% <0.00%> (+1.89%)	⬆️
consensus/lstate/statecastlocal.go	57.10% <0.00%> (+2.18%)	⬆️
consensus/objs/pcn.go	41.30% <0.00%> (+3.26%)	⬆️

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