do not embed keeper interface into keeper struct

[ParthDesai]

• Embedding keeper interface into struct cause interface to be unenforceable at compile time which results in runtime error

[codecov]

Codecov Report

Merging #169 (00f11aa) into main (f435855) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #169   +/-   ##
=======================================
  Coverage   56.37%   56.37%           
=======================================
  Files          15       15           
  Lines        1247     1247           
=======================================
  Hits          703      703           
  Misses        496      496           
  Partials       48       48           

Impacted Files	Coverage Δ
x/gastracker/keeper/keeper.go	69.62% <ø> (ø)

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