src: avoid implicit type conversions

This fixes a bunch of C4244 ('conversion' conversion from 'type1' to
'type2', possible loss of data) MSVC warnings in the code base.

PR-URL: https://github.com/nodejs/node/pull/37149


Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>