Ensure correct disposal with using statement

[bergmeister]

PR Summary

Instead of calling IDisposable.Dispose(), use using statement instead to ensure that Dispose always gets called.
Please use white-space ignoring diff due to the added indentation, some of the existing code looks sub-optimal but I only want to fix this problem where .Dispose() might get called.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
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[rjmholt]

Much nicer