src: apply clang-tidy various improvement

* rewrite to default label in method ConvertUVErrorCode
* improve if condition in method PeekWritable
* remove redundant cast in node_file.cc

PR-URL: https://github.com/nodejs/node/pull/26470


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>