Fix xerrors deprecations

[nervo]

According to xerrors documentation (https://pkg.go.dev/golang.org/x/xerrors) Is and As methods have been deprecated in favor of standard errors package.

This PR:

• Update xerrors to latest version
• Rename internal package internal/errors to just internal to avoid name conflict with standard errors package
• Switch every xerrors.Is / xerrors.As to its standard errors package equivalent

Fix #321

[codecov-commenter]

Codecov Report

Merging #405 (beb76d9) into master (0640a15) will not change coverage.
The diff coverage is 21.88%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #405   +/-   ##
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  Coverage   76.02%   76.02%           
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  Files          13       13           
  Lines        4692     4692           
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  Hits         3567     3567           
  Misses        866      866           
  Partials      259      259