ADD: staking pallet

[coderfengyun]

{Summary}

Fixes #{issue}

Type of change

• [ ] Bug Fix (non-breaking change which fixes an issue)
• [x] New Feature (non-breaking change which adds functionality)
• [ ] Breaking Change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
• [ ] This change requires a storage migration
• [ ] This change requires a benchmark

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] New and existing benchmarks pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings

[codecov-commenter]

Codecov Report

Merging #44 (e6302cd) into main (4b52aaf) will decrease coverage by 0.04%. The diff coverage is 38.51%.

:exclamation: Current head e6302cd differs from pull request most recent head 440c899. Consider uploading reports for the commit 440c899 to get more accurate results

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   41.41%   41.37%   -0.05%     
==========================================
  Files          35       36       +1     
  Lines        2277     2405     +128     
==========================================
+ Hits          943      995      +52     
- Misses       1334     1410      +76     

Impacted Files	Coverage Δ
pallets/stake/src/lib.rs	38.51% <38.51%> (ø)
pallets/nft/src/lib.rs	39.62% <0.00%> (+0.84%)	:arrow_up:

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