Fix WASM Output Parameters for JS TypedArrays

[Adityakk9031]

Fixes #3067

Issue
In the WASM bindings, functions that take a JS TypedArray as an output parameter (like
mj_contactForce
,
mj_jac
, etc.) fail to write data back to the array.

This happens because
unpack.h
was interpreting byteOffset of a JS TypedArray as a raw WASM memory pointer. For user-created TypedArrays (which are not views into the WASM heap), byteOffset is just an offset within a JS ArrayBuffer (often 0), leading to writes to invalid memory addresses instead of the JS array.

Solution
Implemented a Copy-In / Copy-Out mechanism for JS TypedArrays in
unpack.h
:

Copy-In: When a JS TypedArray is passed, its data is copied into a temporary C++ std::vector (using convertJSArrayToNumberVector).
Reference Tracking: A reference to the original JS object is stored in UnpackedParam::source_val_.
Copy-Out: Added a
writeBack()
method to
UnpackedParam
. When called, it copies the data from the temporary C++ vector back into the original JS TypedArray using TypedArray.set().
Binding Update: Updated
mj_contactForce_wrapper
to call
writeBack()
after the underlying C function returns.
Changes
wasm/unpack.h
:
Added source_val_ member to
UnpackedParam
.
Updated
FromValue
to handle JS TypedArrays by copying data and storing the reference.
Added
writeBack()
method to sync data back to JS.
wasm/codegen/generated/bindings.cc
:
Added result_.writeBack() to
mj_contactForce_wrapper
.

[Adityakk9031]

@btaba please look into this pr