fix: copy buffers read from wasm memory

[mhmd-azeez]

By default, Wazero's api.Memory.Read returns a view of the underlying memory:

Write-through

This returns a view of the underlying memory, not a copy. This means any
writes to the slice returned are visible to Wasm, and any updates from
Wasm are visible reading the returned slice.

For example:
buf, _ = memory.Read(offset, byteCount)
buf[1] = 'a' // writes through to memory, meaning Wasm code see 'a'.

If you don't intend-write through, make a copy of the returned slice.

This caused an issue for varSet because it basically set the value of the variable to a view of the underlying memory. And before every call, we call extism_reset to reset the wasm memory. So this would basically zero out the values of all variables.

We have two choices:

1. Copy the buffer in ReadBytes which is what I have done in this PR
2. Copy the buffer in varSet. This allows for fine grain control over reading wasm memory, but it might create similar (hard to track) bugs in the future

[mhmd-azeez]

I have also fixed the JS SDK which had the same problem, the Rust SDK doesn't have this problem

[zshipko]

Good catch!

[mhmd-azeez]

It was all thanks to @bhelx's new count vowels plugin