fix(typescript): clear timeout handle after fetch

[maxceem]

Fixes issue #31

After this fix is applied, repro script outputs as expected:

> start
> node index.mjs

sending request...
response received after 450ms
{"data":{"id":"44196397","name":"Elon Musk","username":"elonmusk"}}
response is already received; if the process hangs, the SDK left something alive
beforeExit after 454ms

[CLAassistant]

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