fix(typescript-fetch): ResponseError prototype chain

[jehiah]

Issue:

ResponseError instances are recognized as Error but not as ResponseError when caught. This occurs because TypeScript (and Babel/ES5 transpilation) doesn't automatically preserve the prototype chain for classes extending Error, causing instanceof ResponseError to fail.

Related: TypeScript wiki on extending Error

Resolution:

Updated the ResponseError, FetchError and RequiredError constructors to explicitly set the prototype

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[jehiah]

cc Typescript Committee Members: @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka @joscha @dennisameling

[cubic-dev-ai]

No issues found across 20 files