Improve error message when npx isn't found on the PATH

[chiually]

Proposed Changes

Previously, when npx was not on the PATH (user does not have node installed on their machine), there would be the following error message and a subprocess would run that would ultimately fail due to the missing requirement.

Now, when npx is not on the path, there is an informative error message telling the user exactly what they are missing. We also raise the error such that the subprocess will not run if npx is not on the PATH.

...

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[coveralls]

Coverage Report for CI Build 35890745288

Coverage remained the same at 90.907%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	4091
Covered Lines:	3719
Line Coverage:	90.91%
Coverage Strength:	17.67 hits per line

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💛 - Coveralls

[david-yz-liu]

Nice work, @chiually!