refactor(nvim): refactor more APIs to use jobrunner.

[Davidyz]

This PR refactors the neovim plugin for #144 .

Note: jobrunners currently don't provide a status code, which makes it difficult to migrate check. The reason is mostly about the LSP runner and will be addressed in future updates.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.25%. Comparing base (2c38a4e) to head (71def5e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #155   +/-   ##
=======================================
  Coverage   99.25%   99.25%           
=======================================
  Files          22       22           
  Lines        1476     1476           
=======================================
  Hits         1465     1465           
  Misses         11       11           

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