feat(tools): add tsx and use it to run scripts

[huyenltnguyen]

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In #97, I added ts-node as it is needed in order to run Jest in TypeScript, and I removed tsx as naive me thought ts-node alone should suffice. Turned out ts-node doesn't work well with ESM, so it's best to use tsx to run scripts.

This PR adds tsx back, and we now:

• Use ts-node only for Jest
• Use tsx to execute scripts

[huyenltnguyen]

Closing in favor of #29.