fix: export ssh_userauth.dart in public API (#188)

[vicajilau]

Closes #188.

This pull request updates the package to version 2.22.5 and improves the public API by exporting user authentication types from dartssh2.dart. It also adds a test to ensure these types are accessible, and updates the changelog accordingly.

Public API changes:

• Exported src/ssh_userauth.dart in lib/dartssh2.dart, making SSHUserInfoRequest, SSHUserInfoPrompt, SSHAuthMethod, and SSHChangePasswordResponse available to library users.

Testing:

• Added test/src/ssh_userauth_export_test.dart to verify that user authentication types are correctly exported and usable from the main library entrypoint.

Documentation:

• Updated CHANGELOG.md to document the export of user authentication types and reference issue.

Versioning:

• Bumped package version to 2.22.5 in pubspec.yaml.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.07%. Comparing base (6213203) to head (6e37986).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #189      +/-   ##
==========================================
+ Coverage   55.92%   56.07%   +0.14%     
==========================================
  Files          66       66              
  Lines        5473     5473              
==========================================
+ Hits         3061     3069       +8     
+ Misses       2412     2404       -8     

Flag	Coverage Δ
unittests	56.07% <ø> (+0.14%)	⬆️

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see 1 file with indirect coverage changes

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