fix: use Call instead of Get+Invoke in fetch to preserve this for service bindings

[akinazuki]

Problem

When using WithBinding to call a Cloudflare Service Binding's fetch method, the current implementation throws:

panic: JavaScript error: Illegal invocation: function called with incorrect `this` reference.

This happens because bind.go detaches the method before calling it:

fetchFunc := namespace.Get("fetch")  // detaches method from object
promise := fetchFunc.Invoke(...)     // this === undefined → Illegal invocation

In JavaScript, obj.method() and const f = obj.method; f() behave differently. The latter loses this, which is required for service binding methods to identify the target Worker.

Fix

Replace Get("fetch").Invoke(...) with Call("fetch", ...), which is equivalent to namespace.fetch(...) in JavaScript and preserves the correct this reference:

promise := namespace.Call("fetch", jsReq, init.ToJS())

This fix works correctly for both the global fetch (where this is globalThis) and service bindings (where this must be the binding object).

Notes

• js.Value.Call(m, args...) is equivalent to JS obj.method(args...) — this is bound to obj
• js.Value.Invoke(args...) is equivalent to JS fn(args...) — this is undefined in strict mode
• The existing DurableObjectStub.Fetch in dostub.go already uses .Call("fetch", ...) correctly; this aligns fetch/bind.go with that pattern

[syumai]

Thanks!