fix: Add error message for running a circuit without instructions

[avawang1]

Issue #, if available:

Description of changes:

• Add error message for running a circuit without instructions. Before, for circuits without any gates (only observables, for example), an uninformative validation error is returned: "max() arg is an empty sequence"

Testing done:

• Added unit tests

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• Commit ID: 25f1258
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[speller26]

Is the check for Sample with shots=0 done somewhere else? I forgot. If it is, does it make sense to move it here?

[avawang1]

There's already a check for that in the default simulator and API. I don't think we need to add a duplicate check here.

[amazon-braket-ci-bot]

AWS CodeBuild CI Report

• CodeBuild project: SDKPullRequestBuild
• Commit ID: 375ffe8
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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