fix(developer): kmcmplib was clobbering previous output

Running kmc on a set of keyboards would sporadically fail after some
time. It turns out this was related to memory allocation, specifically,
resizing the WASM module's memory buffer caused `TypedArray` views into
the memory to be reset!

By default, when a `Uint8Array` is created from an `ArrayBuffer` (e.g.
`Module.HEAP8.buffer`), it is a dynamic view into that buffer. This
module buffer can be dynamically reallocated at any time, which can
happen when allocating memory in WASM code (so the change will look
_really_ weird in a stack trace). Thus, to ensure we don't trip over
ourselves, we need to copy the buffer. Fortunately, creating a
`Uint8Array` from a `Uint8Array` copies the data, and is pretty quick.