chore: consolidate the import declaration of the internal error package

[panjf2000]

No description provided.

[codecov]

Codecov Report

Patch coverage: 46.15% and no project coverage change.

Comparison is base (f7830a4) 76.68% compared to head (bd35ff7) 76.68%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #501   +/-   ##
=======================================
  Coverage   76.68%   76.68%           
=======================================
  Files          25       25           
  Lines        2466     2466           
=======================================
  Hits         1891     1891           
  Misses        435      435           
  Partials      140      140           

Flag	Coverage Δ
unittests	76.68% <46.15%> (ø)

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Files Changed	Coverage Δ
client_unix.go	58.06% <0.00%> (ø)
connection_unix.go	71.56% <0.00%> (ø)
eventloop_unix.go	74.11% <100.00%> (ø)

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