feat: allow v8 alloc for typed-array

[nazarhussain]

Summary

• Add alloc(len) to TypedArray for zero-copy construction into V8 memory
• Pairs with existing toSlice() for direct buffer fill
• Closes Add ergonomic DSL helpers for constructing JS TypedArrays without raw env.createArrayBuffer/createTypedarray boilerplate #19

Example

var arr = try js.Uint8Array.alloc(size);
_ = try view.serializeIntoBytes(try arr.toSlice());
return arr;

[GrapeBaBa]

should we consider add comptime type check since it looks like only support several array_types

[nazarhussain]

We use this struct for shared behavior of the typed arrays, so the new functions added here can be used as js.Uint8Array.alloc() or js.Uint16Array.alloc(). Do not understand what do you mean by further comptime checks.

[nazarhussain]

If needed we can add anytime as a patch.