Add pytest-aiohttp development dep to svi_client

[aaraney]

fixes #217

Additions

• Adds pytest-aiohttp development dependency to svi_client

Testing

1. Verified that this resolves locally RuntimeError: There is no current event loop in thread 'MainThread'. thrown in slow unit tests.

Checklist

• [x] PR has an informative and human-readable title
• [x] PR is well outlined and documented. See #12 for an example
• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows project standards (see CONTRIBUTING.md)
• [x] Passes all existing automated tests
• [x] Any change in functionality is tested
• [x] New functions are documented (with a description, list of inputs, and expected output) using numpy docstring formatting
• [x] Placeholder code is flagged / future todos are captured in comments
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[aaraney]

Weird, looks like a NWMFileProcessor test is failing.

[aaraney]

Looks like the xarray.backends.plugins.list_engines function is throwing a exception because an EntryPoints object doenst have a method im assuming it previously had. Im going to throw this into its own issue and track it there.