`napi` only supports numbers in 16 and 32-bits. To support Rust
numbers with 8 and 16-bits, we can cast them to 32-bits. To convert
from 8 and 16-bits to 32-bits, we use their `Into` implementation. To
convert from 32-bits to 8 and 16-bits, we use their `TryInto`, we
should theorically not fail, but in case of, an `except` message is
appended.
The code has also been re-indented as it was containing a mix of 2
spaces, 4 spaces and tabs identation.
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