Update to TypeScript 5.9 and change return types from Uint8Array to Uint8Array<ArrayBuffer>

[timostamm]

This PR updates the repository from TypeScript 5.6 to 5.9.

Important

TypeScript 5.9 includes breaking changes to lib.d.ts, forcing us to change return types for some functions from Uint8Array to Uint8Array<ArrayBuffer>, most notably toBinary().

If you are on TypeScript 5.7 or later, you will not see any issues, because it already ships with the new type parameter.

If you are on TypeScript 5.6 and earlier, you will be affected by this change: The return type of toBinary() will become any, because the compiler does not understand the Uint8Array<ArrayBuffer> type.

If you see a compiler error TS2315: Type 'Uint8Array' is not generic originating from @bufbuild/protobuf, make sure to set skipLibCheck": true in your tsconfig.json.

The rationale for this change in TypeScript is explained in microsoft/TypeScript#59417: Some APIs accept typed arrays backed by a SharedArrayBuffer, while others only accept ArrayBuffer, and the new version of TypeScript checks the types. For example:

// Invalid because fetch requires an ArrayBuffer. Compile-time error with TS v5.9
fetch("http://example.com", {
  method: "POST",
  body: new Uint8Array(new SharedArrayBuffer(0)),
});

// Valid
fetch("http://example.com", {
  method: "POST",
  body: new Uint8Array(new ArrayBuffer(0)),
});

Because of this interoperability with other APIs, it's necessary that we change our return types.