Migrating SkillMasteryApiService

[Showtim3]

Explanation

Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
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[codecov-io]

Codecov Report

Merging #23 into develop will increase coverage by 0.03%.
The diff coverage is 34.09%.

@@             Coverage Diff             @@
##           develop      #23      +/-   ##
===========================================
+ Coverage    47.81%   47.84%   +0.03%     
===========================================
  Files          850      852       +2     
  Lines        35032    35080      +48     
  Branches      4129     4134       +5     
===========================================
+ Hits         16748    16782      +34     
- Misses       17441    17459      +18     
+ Partials       843      839       -4

Flag	Coverage Δ
#frontend	47.84% <34.09%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
...-page/services/exploration-player-state.service.ts	51.96% <ø> (-0.92%)	⬇️
core/templates/dev/head/pages/Base.ts	25.64% <ø> (+0.64%)	⬆️
...ons/objects/templates/fraction-editor.directive.ts	4.17% <0%> (-1.1%)	⬇️
.../head/pages/library-page/library-page.directive.ts	22.22% <0%> (ø)	⬆️
...ovements-tab/services/improvement-modal.service.ts	6.41% <0%> (-2.68%)	⬇️
core/templates/dev/head/app.constants.ts	100% <100%> (ø)	⬆️
...tics-tab/services/learner-action-render.service.ts	97.67% <100%> (+4.57%)	⬆️
...age/services/audio-translation-language.service.ts	97.01% <100%> (+26.87%)	⬆️
...dev/head/domain/utilities/language-util.service.ts	91.94% <100%> (+0.13%)	⬆️
...ead/domain/exploration/AnswerStatsObjectFactory.ts	100% <100%> (+44.44%)	⬆️
... and 15 more