add unit tests for api-command.ts

[rossiam]

• moved old unit tests file from packages dir into new structure (done as a separate commit)
• rewrote those unit tests for yargs and ESM
• added st-client-wrapper.ts with a couple of very thin wrappers around a couple of classes from the core SDK to make them easier to mock
• default the generic type for SmartThingsCommand to SmartThingsCommandFlags (the minimum necessary) so we don't have to specify it for commands and unit tests that don't add flags

[changeset-bot]

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Latest commit: f67e4a7

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