Export SetContext to support mocking Transport

[bjohnso5]

Description of the change

Export the setContext method of the Transport interface to allow mocking via reimplmentation.

Type of change

(I'm not sure how to categorize this change, if I'm honest - I'm selecting Maintenance)

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

Related issues

Shortcut stories and GitHub issues (delete irrelevant)

• Fix Unexported function on the Transport interface prevents mocking  #104

Checklists

Development

• Lint rules pass locally (I was unable to determine what lint rules this might be referencing)
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer