feat:Added additional exports for IDE and documentation visibility

[alevinetx]

1. Description

Added a few extra classes from under lib/src to the export list in mastodon-api.dart. This will increase IDE visibility and add them to the auto-generated documentation.

No API changes have been made, and there should be no problem in exposing these classes directly.

1.1. Checklist

• [x] The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• [x] I have read the Contributor Guide and followed the process outlined for submitting PRs.
• [x] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples.

1.2. Breaking Change

• [ ] Yes, this is a breaking change.
• [X] No, this is not a breaking change.

1.3. Related Issues

Resolves #94

[codecov-commenter]

Codecov Report

Merging #95 (fa56702) into main (7bc636f) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #95   +/-   ##
=======================================
  Coverage   69.41%   69.41%           
=======================================
  Files          92       92           
  Lines         899      899           
=======================================
  Hits          624      624           
  Misses        275      275           

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