Get rid of require() call in sdks/typescript/ ... /Fetcher.ts

[abcxff]

https://github.com/rivet-gg/rivet/blob/8413349876f7e70d19b0b4a5497d571cf7bcef74/sdks/runtime/typescript/src/core/fetcher/Fetcher.ts#L76

We spoke about this sometime in the past: this breaks the compilation/use of esm modules and it might be better to just assume fetch exists (as it exists by default in node as well)

[linear]

RVT-3805 Get rid of require() call in sdks/typescript/ ... /Fetcher.ts